Receiving apparatus, transmitting apparatus, and reception method

ABSTRACT

Channel fluctuation values on propagation paths of modulated signals transmitted from a plurality of antennas are estimated, an eigenvalue of a channel fluctuation matrix created with the above-mentioned channel fluctuation values as elements is found in order to relate antenna received signals to modulated signals, and using that eigenvalue, receiving antenna selection, combining of modulated signals, and weighting processing on soft decision decoded values, are performed, and modulated signals are demodulated. By this means, it is possible to perform demodulation processing based on the effective reception power of a modulated signal (that is to say, the essential reception power, of the reception power obtained by a receiving apparatus, that can be effectively used when demodulating a modulated signal), enabling the precision of demodulation of modulated signals to be improved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a receiving apparatus,transmitting apparatus, and reception method, and more particularly to areceiving apparatus, transmitting apparatus, and reception methodapplied to a radio communication system that uses multiple antennas.

[0003] 2. Description of the Related Art

[0004] To date, intense research and development has been carried out onradio communication systems that use multiple antennas to allowtransmission and reception of a greater amount of data in a limitedfrequency band. Examples of radio communication systems that usemultiple antennas are a MIMO (Multiple-Input Multiple-Output) system inwhich both the transmitting apparatus and receiving apparatus areequipped with a plurality of antennas, and a MISO (Multiple-InputSingle-Output) system in which the transmitting apparatus is equippedwith a plurality of antennas and the receiving apparatus is equippedwith a single antenna.

[0005] In a radio communication system that uses this kind ofmulti-antenna technology, since modulated signals transmitted from aplurality of antennas are multiplexed on a propagation path and receivedby an antenna at the receiving end, if demodulation processing includingsignal separation processing cannot be carried out with high precisionthe receive data error rate characteristics degrade, and as a result, itis not possible to achieve the original aim of increasing the datatransmission speed.

[0006] Possible ways of improving the precision of separation anddemodulation of each modulated signal include increasing the pilotsymbols inserted in each modulated signal, but when pilot symbols areincreased, propagation efficiency degrades proportionally, with theresult that it is not in fact possible to achieve the original aim ofincreasing the data transmission speed.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a receivingapparatus, transmitting apparatus, and reception method that make itpossible to improve the precision of demodulation including separationprocessing of each modulated signal and improve receive data error ratecharacteristics in a radio communication system that uses multipleantennas.

[0008] The present invention estimates a channel fluctuation value on apropagation path of each modulated signal transmitted from a pluralityof antennas, finds an eigenvalue of a channel fluctuation matrix formedas an above channel fluctuation value element for relating each antennareceived signal to each modulated signal, and using that eigenvalue,performs receiving antenna selection, combining of modulated signals,and weighting processing on a soft decision decoded value, anddemodulates each modulated signal. By this means, it is possible toperform demodulation processing based on the effective reception powerof a modulated signal (that is, the essential reception power, of thereception power obtained by the receiving apparatus, that can beeffectively used when demodulating each modulated signal), therebyenabling the precision of demodulation of each modulated signal to beimproved.

[0009] Also, in a receiving apparatus of the present invention, afurther technique is provided whereby an eigenvalue is found byequalizing the power of each element (channel fluctuation value) of theabove-mentioned channel fluctuation matrix. This means make it possibleto suppress disruption of the relationship between an eigenvalue andeffective reception power occurring due to signal amplificationprocessing or analog-digital conversion processing in the radio section,and to find an eigenvalue that reflects effective reception power farmore accurately. The processing that equalizes the power of each elementof this channel fluctuation matrix also corresponds to findingeigenvalue approximation using only phase of the channel fluctuationmatrix, so that an eigenvalue can be found that accurately reflectseffective power with a small amount of computation.

[0010] Furthermore, a transmitting apparatus of the present inventionprovides independent control for each antenna of the transmission powerof the modulated signal transmitted from each antenna based oninformation such as a channel fluctuation value and received fieldstrength of each modulated signal fed back from the receiving apparatus.By this means, the effective reception power of each modulated signalcan be changed more accurately, enabling the precision of demodulationof each modulated signal in the receiving apparatus to be greatlyimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and other objects and features of the present inventionwill appear more fully hereinafter from a consideration of the followingdescription taken in connection with the accompanying drawings whereinone example is illustrated by way of example, in which:

[0012]FIG. 1 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 1 of thepresent invention;

[0013]FIG. 2 is a block diagram showing a configuration of a receptionunit of a transmitting apparatus of Embodiment 1;

[0014]FIG. 3 is a drawing showing frame configurations of transmitsignals transmitted from a transmission unit of a transmittingapparatus;

[0015]FIG. 4 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 1;

[0016]FIG. 5 is a block diagram showing a configuration of atransmission unit of a receiving apparatus of Embodiment 1;

[0017]FIG. 6 is a drawing showing a frame configuration of a transmitsignal transmitted from a transmission unit of a transmitting apparatus;

[0018]FIG. 7 is a drawing illustrating channel fluctuation betweenantennas of a transmitting apparatus and receiving apparatus;

[0019]FIG. 8 is a block diagram showing another sample configuration ofa transmission unit of a transmitting apparatus;

[0020]FIG. 9 is a block diagram showing a configuration of the spreadingsection in FIG. 8;

[0021]FIG. 10 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 2;

[0022]FIG. 11 is a drawing showing frame configurations of transmitsignals transmitted from the transmission unit in FIG. 10;

[0023]FIG. 12 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 2;

[0024]FIG. 13 is a drawing showing a configuration of the inverseFourier transform section in FIG. 10;

[0025]FIG. 14 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 3;

[0026]FIG. 15 is a block diagram showing a configuration of the antennaselection section in FIG. 14;

[0027]FIG. 16 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 4;

[0028]FIG. 17 is a block diagram showing a configuration of the signalprocessing section in FIG. 16;

[0029]FIG. 18 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 5;

[0030]FIG. 19 is a block diagram showing a configuration of the signalprocessing section in FIG. 18;

[0031]FIG. 20 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 7;

[0032]FIG. 21 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 7;

[0033]FIG. 22 is a drawing showing the signal point arrangement in theIQ plane of a BPSK modulated signal;

[0034]FIG. 23 is a drawing provided for explanation of a BPSK modulatedsignal soft decision value;

[0035]FIG. 24 is a block diagram showing another sample configuration ofa reception unit of a receiving apparatus of Embodiment 7;

[0036]FIG. 25 is a drawing provided for explanation of calculation ofthe distance between a reception point and a candidate point;

[0037]FIG. 26 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 8;

[0038]FIG. 27 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 8;

[0039]FIG. 28 is a block diagram showing another sample configuration ofa reception unit of a receiving apparatus of Embodiment 8;

[0040]FIG. 29 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 9;

[0041]FIG. 30 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 9;

[0042]FIG. 31 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 10;

[0043]FIG. 32 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 10;

[0044]FIG. 33 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 11;

[0045]FIG. 34 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 12;

[0046]FIG. 35 is a drawing showing space-time code frame configurations;

[0047]FIG. 36 is a drawing showing the relationship between transmittingantennas and a receiving antenna when using space-time-coding;

[0048]FIG. 37 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 13;

[0049]FIG. 38 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 13;

[0050]FIG. 39 is a block diagram showing a configuration of the antennaselection section in FIG. 38;

[0051]FIG. 40 is a drawing showing frame configurations when space-timecode is OFDM modulated and transmitted;

[0052]FIG. 41 is a drawing showing time-frequency coding frameconfigurations;

[0053]FIG. 42 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 15;

[0054]FIG. 43 is a drawing showing a configuration of the signalprocessing section in FIG. 42;

[0055]FIG. 44 is a block diagram showing a configuration of atransmission unit of a transmitting apparatus of Embodiment 17;

[0056]FIG. 45 is a block diagram showing a configuration of a receptionunit of a receiving apparatus of Embodiment 17;

[0057]FIG. 46 is a block diagram showing a configuration of a signalprocessing section of Embodiment 18;

[0058]FIG. 47 is a drawing provided for explanation of calculation ofEuclidian distance between a reception point and candidate point;

[0059]FIG. 48 is a block diagram showing a configuration of a signalprocessing section of Embodiment 19; and

[0060]FIG. 49 is a drawing showing simulation results when using theconfiguration of Embodiment 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] The inventors of the present invention arrived at the presentinvention by considering that, in a radio communication system that usesmultiple antennas, the demodulation precision of each modulated signalcan be improved by not simply performing separation and demodulation ofeach modulated signal, but performing demodulation processing andtransmission processing that takes account of the effective receptionpower of a received modulated signal (that is, the essential receptionpower, of the reception power obtained by the receiving apparatus, thatcan be effectively used when demodulating each modulated signal).

[0062] In the present invention, an eigenvalue of a channel fluctuationmatrix is used as an effective reception power index. A channelfluctuation matrix relates each antenna received signal to eachmodulated signal, with channel fluctuation values as elements.Generally, a receiving apparatus used in multi-antenna communicationsfinds the inverse matrix of the channel fluctuation matrix and separateseach modulated signal from the received signal.

[0063] In the present invention, an eigenvalue is found from a generallyused channel fluctuation matrix in this way, and this is used as aneffective reception power index, so that it is possible to find theeffective reception power with comparatively little computation andcomparatively few configuration additions.

[0064] In the following embodiments, the following kinds of modes of thepresent invention are chiefly described.

[0065] In one mode of the present invention, a transmitting apparatusthat transmits a plurality of modulated signals from a plurality ofantennas performs modification of the transmission power of thetransmitted plurality of modulated signals independently for eachantenna. Also, transmission power control is performed using receivedfield strength and channel fluctuation estimated by the communicatingparty. By this means, data transmission quality can be improved.Specifically, it is possible to perform modulated signal transmissionpower control so that effective reception power is optimized, therebyenabling the demodulation precision of each modulated signal on thereceiving side to be improved.

[0066] In another mode of the present invention, a receiving apparatusthat receives a modulated signal transmitted by an above-describedtransmitting apparatus is equipped with a received field strengthestimation section that estimates the received field strength from thereceived signal, and feeds back estimated received field strengthinformation to the transmitting apparatus. The receiving apparatus isalso equipped with a channel fluctuation estimation section thatestimates channel fluctuation of each modulated signal from a receivedsignal, and feeds back estimated channel fluctuation information to thetransmitting apparatus. By this means, a transmitting apparatus canperform modulated signal transmission power control based on receivedfield strength information and channel fluctuation information so thateffective reception power actually becomes optimal on the receivingside.

[0067] In yet another mode of the present invention, a transmittingapparatus that transmits modulated signals from a plurality of antennasusing a multi-antenna system performs modification of the transmissionpower of the transmitted plurality of modulated signals independentlyfor each antenna and independently for each carrier. Also, thetransmitting apparatus performs this transmission power control usingper-carrier received field strength and per-carrier channel fluctuationestimated by the communicating party. By this means, it is possible toperform modulated signal transmission power control so that effectivereception power becomes optimal independently for each antenna andindependently for each carrier.

[0068] In yet another mode of the present invention, a receivingapparatus that receives a modulated signal transmitted by anabove-described multicarrier transmitting apparatus is equipped with areceived field strength estimation section that estimates per-carrierreceived field strength from the received signal, and feeds backestimated per-carrier received field strength information to themulticarrier transmitting apparatus. The receiving apparatus is alsoequipped with a channel fluctuation estimation section that estimateschannel fluctuation for each carrier from a received signal, and feedsback estimated per-carrier channel fluctuation information to themulticarrier transmitting apparatus. By this means, a multicarriertransmitting apparatus can perform modulated signal transmission powercontrol for each carrier based on per-carrier received field strengthinformation and channel fluctuation information so that effectivereception power actually becomes optimal on the receiving side.

[0069] In yet another mode of the present invention, a receivingapparatus that receives a plurality of modulated signals transmittedfrom a plurality of antennas with a plurality of receiving antennasgreater than the plurality of transmitting antennas, creates a a channelfluctuation matrix for each combination, creates a channel fluctuationmatrix eigenvalue for each combination, selects the antenna receivedsignals of the combination whose eigenvalue minimum power is thegreatest, and performs demodulation processing. By this means, eachmodulated signal can be demodulated using the antenna received signalcombination with the greatest modulated signal effective receptionpower, thereby enabling modulated signal demodulation precision to beimproved compared with the case where each modulated signal isdemodulated using all antenna received signals.

[0070] In yet another mode of the present invention, a receivingapparatus that receives a plurality of modulated signals transmittedfrom a plurality of antennas with a plurality of receiving antennasgreater than the plurality of transmitting antennas, creates a pluralityof antenna received signal combinations, forms a channel fluctuationmatrix for each combination, and calculates creates a channelfluctuation matrix eigenvalue for each combination. The receivingapparatus then separates each modulated signal using each combination ofantenna received signals and the channel fluctuation matrixcorresponding to that combination, and also weights and combinesmodulated signals separated in each combination using the channelfluctuation matrix eigenvalues used at the time of separation. By thismeans, it is possible to perform weighting and combining of eachmodulated signal according to the modulated signal effective receptionpower, thereby enabling modulated signal demodulation precision to beimproved.

[0071] In yet another mode of the present invention, a receivingapparatus that receives a plurality of modulated signals subjected toerror correction coding and transmitted from a plurality of antennas isequipped with a soft decision value calculation section that finds achannel fluctuation matrix eigenvalue, and finds a soft decision valuefrom this eigenvalue and a received quadrature baseband signal.

[0072] In yet another mode of the present invention, a receivingapparatus that receives a plurality of modulated signals subjected toerror correction coding and transmitted from a plurality of antennas isequipped with a soft decision value calculation section that finds aneffective reception level from a reception level and a channelfluctuation matrix eigenvalue, and finds a soft decision value from thiseffective reception level and a received quadrature baseband signal.

[0073] By performing calculation by weighting a soft decision value withan effective reception level in this way, it is possible to give a softdecision value an appropriate likelihood, and modulated signaldemodulation precision can be improved.

[0074] In yet another mode of the present invention, when demodulationprocessing is performed using a channel fluctuation matrix eigenvalue,control of the reception level of the received signal received at eachantenna is carried out in common for each antenna. By this means, aneigenvalue is found more exactly, so that demodulation processing can beperformed based on an eigenvalue that reflects effective reception powermuch more accurately, thereby enabling the demodulation precision ofeach modulated signal to be greatly improved.

[0075] With reference now to the accompanying drawings, embodiments ofthe present invention will be explained in detail below.

[0076] (Embodiment 1)

[0077] In Embodiment 1, a transmitting apparatus is described thatindependently modifies the transmission power of a modulated signaltransmitted from each antenna.

[0078]FIG. 1 shows a sample configuration of the transmission unit of atransmitting apparatus according to this embodiment, as provided in aradio base station (hereinafter referred to simply as “base station”),for example. Modulation section 102 of transmission unit 100 has atransmit digital signal 101 and timing signal 122 as input, forms atransmit quadrature baseband signal 103 by executing orthogonalmodulation processing such as QPSK (Quadrature Phase Shift Keying) or16QAM (Quadrature Amplitude Modulation) on transmit digital signal 101and performing frame configuration in accordance with timing signal 122(FIG. 3(A)), and outputs this transmit quadrature baseband signal 103. Asignal 103 as input, forms a spread signal 105 by executing spreadingprocessing on this transmit quadrature baseband signal 103 using apredetermined spreading code, and outputs this spread signal 105. Aradio section 106 has spread signal 105 as input, forms a modulatedsignal 107 by executing predetermined radio processing such asdigital-analog conversion processing and up-conversion on spread signal105, and outputs this modulated signal 107.

[0079] A transmission power modification section 108 has modulatedsignal 107, a coefficient 125 found from the reception power, and acoefficient 124 found from an eigenvalue as input, obtains a transmitsignal 109 by multiplying modulated signal 107 by coefficients 125 and124, and outputs this transmit signal 109. By this means, thetransmission power of modulated signal 107 is determined based on thereception power and eigenvalue. Transmit signal 109 is output as a radiowave from an antenna 110.

[0080] Modulation section 112 has a transmit digital signal 111 andtiming signal 122 as input, forms a transmit quadrature baseband signal113 by executing orthogonal modulation processing such as QPSK or 16 QAMon transmit digital signal 111 and performing frame configuration inaccordance with timing signal 122 (FIG. 3(B)), and outputs this transmitquadrature baseband signal 113. A spreading section 114 has transmitquadrature baseband signal 113 as input, forms a spread signal 115 byexecuting spreading processing on this transmit quadrature basebandsignal 113 using a predetermined, spreading code, and outputs thisspread signal 115. Spreading section 114 performs spreading processingusing a different spreading code from that used by spreading section104. A radio section 116 has spread signal 115 as input, forms amodulated signal 117 by executing predetermined radio processing such asdigital-analog conversion processing and up-conversion on spread signal115, and outputs this modulated signal 117.

[0081] A transmission power modification section 118 has modulatedsignal 117, a coefficient 126 found from the reception power, andcoefficient 124 found from an eigenvalue as input, obtains a transmitsignal 119 by multiplying modulated signal 117 by coefficients 125 and124, and outputs this transmit signal 119. By this means, thetransmission power of modulated signal 117 is determined based on thereception power and eigenvalue. Transmit signal 119 is output as a radiowave from an antenna 120.

[0082] Thus, in transmission unit 100 provided in a transmittingapparatus according to this embodiment, it is possible to modifyindependently the transmission power of modulated signals transmittedfrom antennas 110 and 120.

[0083]FIG. 2 shows a sample configuration of the reception unit of atransmitting apparatus according to this embodiment. Reception unit 200is provided in the same base station as transmission unit 100 shown inFIG. 1. Radio section 203 of reception unit 200 has a received signal202 received by an antenna 201 as input, forms a received quadraturebaseband signal 204 by executing predetermined radio processing such asdown-conversion and analog-digital conversion on received signal 202,and outputs this received quadrature baseband signal 204. A demodulationsection 205 has received quadrature baseband signal 204 as input, formsa received digital signal 206 by executing orthogonal demodulationprocessing such as QPSK demodulation or 16QAM demodulation on receivedquadrature baseband signal 204, and outputs this received digital signal206.

[0084] A data separation section 207 has received digital signal 206 asinput, separates received digital signal 206 into data 208, fieldstrength estimation information 209, and channel fluctuation estimationinformation 210, and outputs this data 208, field strength estimationinformation 209, and channel fluctuation estimation information 210.

[0085] A reception power based coefficient calculation section 211 hasfield strength estimation information 209 as input, calculatescoefficients 125 and 126 to be used by transmission power modificationsections 108 and 118 of transmission unit 100 based on this fieldstrength estimation information 209, and sends coefficients 125 and 126to transmission power modification sections 108 and 118. The method offinding these coefficients 125 and 126 will be described in detail laterherein.

[0086] An eigenvalue based coefficient calculation section 214 haschannel fluctuation estimation information 210 as input, calculatescoefficient 124 to be used by transmission power modification sections108 and 118 of transmission unit 100 based on this channel fluctuationestimation information 210, and sends coefficient 124 to transmissionpower modification sections 108 and 118. The method of finding thiscoefficient 124 will be described in detail later herein.

[0087]FIG. 3 shows sample frame configurations on the time axis oftransmit signals 109 (spread signal A) and 119 (spread signal B)transmitted from antennas 110 and 120 of transmission unit 100. Spreadsignal A shown in FIG. 3(A) and spread signal B shown in FIG. 3(B) aretransmitted from antennas 110 and 120 simultaneously. Channel estimationsymbols 301 of spread signal A and channel estimation symbols 301 ofspread signal B are, for example, mutually orthogonalized codes, anditems that can be separated in the reception unit of a terminal are usedfor this purpose. By this means, a terminal reception unit can estimatechannel fluctuation of signals transmitted from antennas 110 and 120based on channel estimation symbols 301 contained in spread signals Aand B.

[0088]FIG. 4 shows a sample configuration of the reception unit of areceiving apparatus according to this embodiment. Reception unit 400 isprovided in a communication terminal, and receives and demodulates asignal transmitted from transmission unit 100 in FIG. 1. Radio section403 of reception unit 400 has a received signal 402 received by anantenna 401 as input, forms a received quadrature baseband signal 404 byexecuting predetermined radio processing such as down-conversion andanalog-digital conversion on received signal 402, and outputs thisreceived quadrature baseband signal 404. A despreading section 405 hasreceived quadrature baseband signal 404 as input, forms a despreadreceived quadrature baseband signal 406 by executing despreadingprocessing using the same spreading code as that used by spreadingsection 104 and spreading section 114 in FIG. 1 on received quadraturebaseband signal 404, and outputs this despread received quadraturebaseband signal 406.

[0089] A spread signal A channel fluctuation estimation section 407 hasdespread received quadrature baseband signal 406 as input, estimateschannel fluctuation of spread signal A (the spread signal transmittedfrom antenna 110) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 408. By this means, channelfluctuation between antenna 110 and antenna 401 is estimated. A spreadsignal B channel fluctuation estimation section 409 has despreadreceived quadrature baseband signal 406 as input, estimates channelfluctuation of spread signal B (the spread signal transmitted fromantenna 120) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 410. By this means, channelfluctuation between antenna 120 and antenna 401 is estimated.

[0090] Radio section 413 has a received signal 412 received by anantenna 411 as input, forms a received quadrature baseband signal 414 byexecuting predetermined radio processing such as down-conversion andanalog-digital conversion on received signal 412, and outputs thisreceived quadrature baseband signal 414. A despreading section 415 hasreceived quadrature baseband signal 414 as input, forms a despreadreceived quadrature baseband signal 416 by executing despreadingprocessing using the same spreading code as that used by spreadingsection 104 and spreading section 114 in FIG. 1 on received quadraturebaseband signal 414, and outputs this despread received quadraturebaseband signal 416.

[0091] A spread signal A channel fluctuation estimation section 417 hasdespread received quadrature baseband signal 416 as input, estimateschannel fluctuation of spread signal A (the spread signal transmittedfrom antenna 110) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 418. By this means, channelfluctuation between antenna 110 and antenna 411 is estimated. A spreadsignal B channel fluctuation estimation section 419 has despreadreceived quadrature baseband signal 416 as input, estimates channelfluctuation of spread signal B (the spread signal transmitted fromantenna 120) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 420. By this means, channelfluctuation between antenna 120 and antenna 411 is estimated.

[0092] A signal processing section 421 has received quadrature basebandsignals 406 and 416, spread signal A channel fluctuation estimationsignals 408 and 418, and spread signal B channel fluctuation estimationsignals 410 and 420 as input, and outputs a spread signal A receivedquadrature baseband signal 422 and spread signal B received quadraturebaseband signal 423 by performing computation using an inverse matrix ofa channel fluctuation matrix with channel fluctuation estimation values408, 410, 418, and 420 as elements. Details of this channel fluctuationmatrix will be given later herein.

[0093] A received field strength estimation section 424 has receivedquadrature baseband signals 406 and 416 as input, finds the receivedfield strength of these signals, and outputs received field strengthestimation information 425. In this embodiment, the received fieldstrength is found from received quadrature baseband signals, but this isnot a limitation, and the received field strength may also be found froma received signal. Also, the received field strength may be foundseparately for spread signal A and spread signal B, or the combined wavereceived field strength may be found.

[0094] A channel fluctuation information generation section 426 hasspread signal A channel fluctuation estimation signals 408 and 418, andspread signal B channel fluctuation estimation signals 410 and 420, asinput, and forms and outputs channel fluctuation estimation information427.

[0095]FIG. 5 shows a sample configuration of the transmission unit of areceiving apparatus according to this embodiment. Transmission unit 500is provided in the same communication terminal as reception unit 400.Information generation section 504 of transmission unit 500 has data501, received field strength estimation information 425, and channelfluctuation estimation information 427 as input, arranges these in apredetermined sequence, and outputs a transmit digital signal 505. Amodulated signal generation section 506 has transmit digital signal 505as input, forms a modulated signal 507 by executing modulationprocessing on transmit digital signal 505, and outputs this modulatedsignal 507. A radio section 508 has modulated signal 507 as input, formsa transmit signal 509 by executing predetermined radio processing suchas digital-analog conversion processing and up-conversion on modulatedsignal 507, and outputs this transmit signal 509. Transmit signal 509 isoutput as a radio wave from an antenna 510.

[0096]FIG. 6 shows a sample frame configuration of a transmit signaltransmitted from transmission unit 500. In FIG. 6, reference numeral 601denotes channel fluctuation estimation information symbols, referencenumeral 602 denotes field strength estimation information symbols, andreference numeral 603 denotes data symbols.

[0097]FIG. 7 shows an example of the relationship between transmitsignals and received signals. Modulated signal Ta(t) transmitted fromtransmitting antenna 110 is received by antennas 401 and 402 after beingsubjected to channel fluctuations h11(t) and h12(t). Modulated signalTb(t) transmitted from transmitting antenna 120 is received by antennas401 and 402 after being subjected to channel fluctuations h21(t) andh22(t).

[0098] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail using FIG.1 through FIG. 7.

[0099] First, the transmission operation of a base station (transmittingapparatus) will be described. An important operation by transmissionunit 100 of the base station apparatus shown in FIG. 1 is to control thetransmission power of modulated signals transmitted from antennas 110and 120 independently at antennas 110 and 120. For this purpose,transmit signals are multiplied by a coefficient in transmission powermodification sections 108 and 118 in transmission unit 100.

[0100] The operation of transmission power modification section 108 willbe described in detail here. If the value of multiplication coefficient125 found from the reception power is designated Ca, modulated signal107 is designated Xa(t), and coefficient 124 found from an eigenvalue isdesignated D, transmission power modification section 108 controlstransmission power Xa′(t) of transmit signal 109 as shown by thefollowing equation.

[0101] [Equation 1]

Xa′(t)=Ca×D×Xa(t)   (1)

[0102] Similarly, if the value of multiplication coefficient 126 foundfrom the reception power is designated Cb, modulated signal 117 isdesignated Xb(t), and coefficient 124 found from an eigenvalue isdesignated D, transmission power modification section 118 controlstransmission power Xb′ (t) of transmit signal 119 as shown by thefollowing equation.

[0103] [Equation 2]

Xb′(t)=Cb×D×Xb(t)   (2)

[0104] Performing transmission power control independently for eachtransmitting antenna in this way enables reception quality to beimproved. Also, reception quality can be much more effectively improvedby performing multiplication by coefficient 124 value D found from aneigenvalue in common in transmission power modification sections 108 and118 of both transmitting antennas. This is because a coefficientobtained from an eigenvalue corresponds to the effective received fieldstrength of a receiving terminal (the actual reception field strength,of the reception field strength obtained by a terminal, that can beeffectively used).

[0105] Moreover, reception quality can be much more effectively improvedby performing multiplication independently by a coefficient found fromreception power in transmission power modification sections 108 and 118of both transmitting antennas. This is because a coefficient obtainedfrom reception power corresponds to transmission power control forimproving the received field strength of each modulated signal at anantenna of a receiving terminal.

[0106] Next, the reception operation of a base station (transmittingapparatus) will be described. If, as shown in FIG. 7, t indicates time,the modulated signal from antenna 110 is designated Ta(t), the modulatedsignal from antenna 120 is designated Tb(t), the received signal atantenna 401 is designated R1(t), the received signal at antenna 402 isdesignated R2(t), and channel fluctuations are designated h11(t),h12(t), h21(t), and h22(t), the relationship shown by the followingequation applies. That is to say, antenna received signals R1(t) andR2(t), and modulated signals Ta(t) and Tb(t), can be related by means ofa channel fluctuation matrix with channel fluctuation values h11(t),h12(t), h21(t), and h22(t) as elements.

[0107] [Equation 3] $\begin{matrix}{\begin{pmatrix}{{R1}(t)} \\{{R2}(t)}\end{pmatrix} = {\begin{pmatrix}{{h11}(t)} & {{h12}(t)} \\{{h21}(t)} & {{h22}(t)}\end{pmatrix}\begin{pmatrix}{{Ta}(t)} \\{{Tb}(t)}\end{pmatrix}}} & (3)\end{matrix}$

[0108] Reception power based coefficient calculation section 211provided in reception unit 200 of the base station (transmittingapparatus) in FIG. 2 determines coefficients 125 and 126 using fieldstrength estimation information 209 received from the terminal—that is,the received field strengths of R1(t) and R2(t)—and channel fluctuationestimation information 210—that is, h11(t), h12(t), h21(t), and h22(t).

[0109] For example, coefficient 125 is found from h11(t) and h21(t)estimates. This is because h11(t) and h12(t) are fluctuation valuesdetermined by the transmission power of the signal output from antenna110 in FIG. 1. Similarly, coefficient 126 is found from h12(t) andh22(t) estimates, because h12(t) and h22(t) are fluctuation valuesdetermined by the transmission power of the signal output from antenna120 in FIG. 1.

[0110] That is to say, the received field strength of R1(t) and R2(t) isthe field strength of a signal in which both the signal from antenna 110and the signal from antenna 120 are combined, and therefore ifcoefficients 125 and 126 are determined based only on that receivedfield strength, this will be insufficient to adjust the signal powerfrom each antenna appropriately. Thus, in this embodiment, in additionto the received field strength, coefficients 125 and 126 for controllingthe signal power transmitted from antennas 110 and 120 are determinedusing channel fluctuation values h11(t), h12(t), h21(t), and h22(t) atthe time of reception of each transmit signal. By this means, the powerat the time of reception of each signal transmitted from antennas 110and 120 can be made appropriate.

[0111] To given an explanation in concrete terms, when the receivedfield strength is low, the values of coefficients 125 and 126 arenaturally made larger so that transmission power increases. Also, thesmaller the magnitude of channel fluctuation values h11(t) and h21(t),the larger the value of coefficient 125 used by antenna 110 is made.Similarly, the smaller the magnitude of channel fluctuation valuesh12(t) and h22(t), the larger the value of coefficient 126 used byantenna 120 is made.

[0112] Eigenvalue based coefficient calculation section 214 calculatesan eigenvalue of the Equation (3) channel fluctuation matrix withchannel fluctuation values h11(t), h12(t), h21(t), and h22(t) receivedfrom the terminal as elements, and finds coefficient 124 based on thevalue with the lowest power among the eigenvalue power figures.

[0113] Calculation methods for finding an eigenvalue here include, forexample, the Jacobi method, Givens method, Housefolde method, QR method,QL method, QL method with implicit shift, and inverse iteration method,any of which may be used in the present invention. Also, eigenvaluepower is a value expressed by a²+b² when an eigenvalue is expressed inthe form a+bj (where a and b are real numbers and j is an imaginarynumber). The same applies to other embodiments described hereinafter.

[0114] Next, the reception operation of a communication terminal(receiving apparatus) will be described. Spread signal A channelfluctuation estimation section 407 of reception unit 400 in FIG. 4estimates spread signal A channel fluctuation—that is, h11(t) inEquation (3)—from spread signal A channel estimation symbols 301 shownin FIG. 3(A), and outputs the estimation result as spread signal Achannel fluctuation estimation signal 408. Spread signal B channelfluctuation estimation section 409 estimates spread signal B channelfluctuation—that is, h12(t) in Equation (3)—from spread signal B channelestimation symbols 301 shown in FIG. 3(B), and outputs the estimationresult as spread signal B channel fluctuation estimation signal 410.

[0115] Spread signal A channel fluctuation estimation section 417estimates spread signal A channel fluctuation—that is, h21(t) inEquation (3)—from spread signal A channel estimation symbols 301 shownin FIG. 3 (A), and outputs the estimation result as spread signal Achannel fluctuation estimation signal 418. Spread signal B channelfluctuation estimation section 419 estimates spread signal B channelfluctuation—that is, h22(t) in Equation (3)—from spread signal B channelestimation symbols 301 shown in FIG. 3 (B), and outputs the estimationresult as spread signal B channel fluctuation estimation signal 420.

[0116] Signal processing section 421 finds spread signal A and Breceived quadrature baseband signals 422 and 423 by performing aninverse matrix operation that multiplies the inverse matrix of thechannel fluctuation matrix by both sides in Equation (3). By this means,received quadrature baseband signal 422 and received quadrature basebandsignal 423 are separated. Channel fluctuation information generationsection 426 has spread signal A channel fluctuation estimation signals408 and 418, spread signal B channel fluctuation estimation signals 410and 420, and estimated channel fluctuations h11(t), h12(t), h21(t), andh22(t) as input, and outputs these as channel fluctuation estimationinformation 427.

[0117] Thus, according to the above configuration, in a transmittingapparatus that performs multi-antenna transmission it is possible tomake the received field strength at the time of reception of eachmodulated signal appropriate, and thus improve the reception quality ofeach modulated signal, by receiving from the communicating stationchannel fluctuation values h11(t), h12(t), h21(t), and h22(t) at thetime of reception of each modulated signal transmitted from antennas 110and 120, and independently controlling at antennas 110 and 120 thetransmission power of modulated signals transmitted from antennas 110and 120 based on these channel fluctuation values h11(t), h12(t),h21(t), and h22(t).

[0118] In addition, by controlling transmission power in considerationof an eigenvalue of a channel fluctuation matrix with channelfluctuation values h11(t), h12(t), h21(t), and h22(t) as elements, theeffective received field strength can be increased, enabling thereception quality of each modulated signal to be greatly improved.

[0119] In the above-described embodiment, a case has been described inwhich coefficients 124, 125, and 126 for controlling the transmissionpower of antennas 110 and 120 are decided by a base station—that is, onthe transmitting side—but the present invention is not limited to this,and it is also possible for coefficients 124, 125, and 126 to be decidedby a terminal—that is, on the receiving side—and for the decidedcoefficients to be fed back to the transmitting side. This also appliesto other embodiments described hereinafter.

[0120] Also, in the above-described embodiment, a case has beendescribed in which the number of antennas is two and the number ofmultiplexed modulated signals is two, but the present invention is notlimited to this, and the present invention can be widely applied tocases where a plurality of antennas are used and a different modulatedsignal is transmitted from each antenna. It is also possible, forexample, for one antenna (for example, antenna 110) that transmits amodulated signal to be configured from a plurality of antennas, as withan adaptive array antenna. This also applies to other embodimentsdescribed hereinafter.

[0121] Moreover, in the above-described embodiment, received fieldstrength has been mentioned, but the present invention may also besimilarly implemented with reception level, reception strength,reception power, reception amplitude, carrier power to noise power, orthe like, substituted for received field strength. This also applies toother embodiments described hereinafter.

[0122] Furthermore, in the above-described embodiment, symbolstransmitted for estimating channel fluctuation are referred to aschannel estimation symbols 301 (FIG. 3), but channel estimation symbols301 may also be referred to as pilot symbols, a preamble, controlsymbols, known symbols, or a unique word, or may be referred to byanother name. Also, channel fluctuation estimation information symbols601 and field strength estimation information symbols 602 in FIG. 6 mayalso be referred to as control symbols, or may be referred to by anothername. In other words, the present invention can be implemented in thesame way as in the above-described embodiment even if these symbols areused. This also applies to other embodiments described hereinafter.

[0123] Moreover, in the above-described embodiment, a spread spectrumcommunication system has been described by way of example, but this isnot a limitation, and the present invention can be similarly implementedin a single-carrier system that does not have a spreading section, or anOFDM system, for example. In the case of a single-carrier system, theconfiguration does not include spreading sections 104 and 114 (FIG. 1)or despreading sections 405 and 415 (FIG. 4). A case in which thepresent invention is applied to an OFDM system is described in detail inEmbodiment 2.

[0124] Furthermore, the configurations of a transmitting apparatus andreceiving apparatus of the present invention are not limited to theconfigurations in FIG. 1, FIG. 2, FIG. 4, and FIG. 5. For example, inthe above-described embodiment a case has been described in whichtransmission power modification sections 108 and 118 are provided, andtransmission power of modulated signals transmitted from antennas 110and 120 is controlled independently by these transmission powermodification sections at antennas 110 and 120 based on coefficient 124found from an eigenvalue and coefficients 125 and 126 found fromreception power, but it is essential only that the modulated signal ofeach antenna be controlled independently, and the configuration is notlimited to that shown in FIG. 1.

[0125]FIG. 8 shows another sample configuration of the transmission unitof a base station according to this embodiment. In FIG. 8, parts thatoperate in the same way as in transmission unit 100 in FIG. 1 areassigned the same codes as in FIG. 1. The difference betweentransmission unit 700 in FIG. 8 and transmission unit 100 in FIG. 1 isthat, whereas transmission unit 100 in FIG. 1 controls the power ofmodulated signals transmitted from each antenna by means of transmissionpower modification sections 108 and 118, transmission unit 700 in FIG. 8controls the power of modulated signals transmitted from each antenna bymeans of spreading sections 701 and 702.

[0126] Specifically, spreading section 701 has transmit quadraturebaseband signal 103, coefficient 125 found from reception power, andcoefficient 124 found from an eigenvalue as input, and outputs spreadsignal 105 of power in accordance with these coefficients 125 and 124.Similarly, spreading section 702 has transmit quadrature baseband signal113, coefficient 126 found from reception power, and coefficient 124found from an eigenvalue as input, and outputs spread signal 115 ofpower in accordance with these coefficients 126 and 124.

[0127]FIG. 9 shows a sample configuration of spreading sections 701 and702. A spreading function section 804 has channel X transmit quadraturebaseband signal 801, channel Y transmit quadrature baseband signal 802,and channel Z transmit quadrature baseband signal 803 as input, forms achannel X spread signal 805, channel Y spread signal 806, and channel Zspread signal 807 by performing spreading processing on these signalsusing different spreading codes, and outputs spread signals 805, 806,and 807. Here, a channel X signal denotes a signal destined for terminalX, a channel Y signal denotes a signal destined for terminal Y, and achannel Z signal denotes a signal destined for terminal Z. That is tosay, transmission unit 700 outputs spread modulated signals destined forthree terminals, X, Y, and Z, respectively from antennas 110 and 120.

[0128] A coefficient multiplication function section 810 has channel Xspread signal 805, channel Y spread signal 806, channel Z spread signal807, coefficient 125 (126) found from reception power, and coefficient124 found from an eigenvalue as input, forms apost-coefficient-multiplication channel X spread signal 811,post-coefficient-multiplication channel Y spread signal 812, andpost-coefficient-multiplication channel Z spread signal 813 byperforming coefficient multiplication in accordance with thesecoefficients 125 (126) and 124, and outputs these signals 811, 812, and813.

[0129] Here, coefficient 125 (126) found from reception power andcoefficient 124 found from an eigenvalue multiplied by channel X spreadsignal 805 are found based on received field strength estimationinformation and channel fluctuation estimation information sent fromterminal X; coefficient 125 (126) found from reception power andcoefficient 124 found from an eigenvalue multiplied by channel Y spreadsignal 806 are found based on received field strength estimationinformation and channel fluctuation estimation information sent fromterminal Y; and coefficient 125 (126) found from reception power andcoefficient 124 found from an eigenvalue multiplied by channel Z spreadsignal 807 are found based on received field strength estimationinformation and channel fluctuation estimation information sent fromterminal Z.

[0130] An addition function section 814 addspost-coefficient-multiplication channel X spread signal 811,post-coefficient-multiplication channel Y spread signal 812, andpost-coefficient-multiplication channel Z spread signal 813, and outputsthe result as spread signal 105 (115).

[0131] In this way, transmission unit 700 simultaneously generatestransmit signals destined for a plurality of terminals. At this time,transmission unit 700 can control transmission power independently foreach antenna and independently for the modulated signals destined foreach terminal by receiving field strength estimation information andchannel fluctuation estimation information from each terminal, finding acoefficient found from reception power and a coefficient found from aneigenvalue for each terminal, and multiplying these coefficientsdiffering for each terminal by the spread modulated signal destined foreach terminal. As a result, when modulated signals destined for aplurality of terminals are transmitted from a plurality of antennas, itis possible to optimize the effective reception power at all of theplurality of terminals, and improve the reception quality of all of theplurality of terminals without reducing transmission speed.

[0132] Thus, according to this embodiment, by receiving informationconstituting an effective reception power index such as channelfluctuation information and received field strength information from areceiving apparatus as feedback information, and modifying the receptionpower of the modulated signal transmitted from each antennaindependently for each antenna based on this information, it is possibleto increase the effective reception power of the modulated signaltransmitted from each antenna, and to implement a transmitting apparatusthat enables modulated signal reception quality to be improved.

[0133] (Embodiment 2)

[0134] In this embodiment, a transmitting apparatus is described thatmodifies the transmission power of a modulated signal transmitted fromeach antenna independently at each antenna and independently for eachcarrier.

[0135]FIG. 10 shows a sample configuration of the transmission unit of atransmitting apparatus according to this embodiment. Transmission unit1000 is provided in a base station apparatus, for example. The basestation reception unit is configured as shown in FIG. 2, for example,the transmission unit of a terminal that performs communication with thebase station is configured as shown in FIG. 5, for example, and theframe configuration of a transmit signal transmitted from the terminaltransmission unit is as shown in FIG. 6, for example. As these havealready been described in Embodiment 1, a description thereof is omittedhere.

[0136] In transmission unit 1000, transmit digital signal 101 and timingsignal 122 are input to modulation section 102, a transmit quadraturebaseband signal group 103 is formed by executing orthogonal modulationprocessing such as QPSK or 16 QAM on transmit digital signal 101 andperforming frame configuration in accordance with timing signal 122(FIG. 11(A)), and transmit orthogonal baseband group 103 is output. AnIDFT 1001 has transmit orthogonal baseband group 103, coefficient 125found from reception power, and coefficient 124 found from an eigenvalueas input, modifies the transmission power based on coefficients 125 and124 and also performs an inverse Fourier transform, and outputs apost-inverse-Fourier-transform signal 1002.

[0137] Similarly, in transmission unit 1000, transmit digital signal 111and timing signal 122 are input to modulation section 112, a transmitquadrature baseband signal group 113 is formed by executing orthogonalmodulation processing such as QPSK or 16QAM on transmit digital signal111 and performing frame configuration in accordance with timing signal122 (FIG. 11(B)), and transmit orthogonal baseband group 113 is output.An IDFT 1003 has transmit orthogonal baseband group 113, coefficient 126found from reception power, and coefficient 124 found from an eigenvalueas input, modifies the transmission power based on coefficients 126 and124 and also performs an inverse Fourier transform, and outputs apost-inverse-Fourier-transform signal 1004.

[0138]FIG. 11 shows sample frame configurations of modulated signalstransmitted from transmission unit 1000. FIG. 11(A) shows the frameconfiguration of a signal transmitted from antenna 110 (channel A), andFIG. 11(B) shows the frame configuration of a signal transmitted fromantenna 120 (channel B). In this example, estimation symbols 1101 aretransmitted at specific time 1 arranged on all subcarriers, andinformation symbols 1102 are transmitted at other times 2 through 9.

[0139]FIG. 12 shows a sample configuration of the reception unit of areceiving apparatus according to this embodiment. Reception unit 1200 isprovided in a communication terminal, and receives and demodulatessignals transmitted from transmission unit 1000 in FIG. 10. Radiosection 1203 of reception unit 1200 has a received signal 1202 receivedby an antenna 1201 as input, forms a received quadrature baseband signal1204 by executing predetermined radio processing such as down-conversionand analog-digital conversion on received signal 1202, and outputs thisreceived quadrature baseband signal 1204. A Fourier transform section(dft) 1205 has received quadrature baseband signal 1204 as input, formsa post-Fourier-transform signal 1206 by executing Fourier transformprocessing on received quadrature baseband signal 1204, and outputs thispost-Fourier-transform signal 1206.

[0140] A channel A channel fluctuation estimation section 1207 haspost-Fourier-transform signal 1206 as input, estimates channelfluctuation of the channel A signal (the OFDM signal transmitted fromantenna 110) based on the channel A channel estimation symbols, andoutputs a channel fluctuation estimation group signal 1208. By thismeans, channel fluctuation between antenna 110 and antenna 1201 isestimated. A channel B channel fluctuation estimation section 1209 haspost-Fourier-transform signal 1206 as input, estimates channelfluctuation of the channel B signal (the OFDM signal transmitted fromantenna 120) based on the channel B channel estimation symbols, andoutputs a channel fluctuation estimation group signal 1210. By thismeans, channel fluctuation between antenna 120 and antenna 1201 isestimated.

[0141] A radio section 1213 has a received signal 1212 received by anantenna 1211 as input, forms a received quadrature baseband signal 1214by executing predetermined radio processing such as down-conversion andanalog-digital conversion on received signal 1212, and outputs thisreceived quadrature baseband signal 1214. A Fourier transform section(dft) 1215 has received quadrature baseband signal 1214 as input, formsa post-Fourier-transform signal 1216 by executing Fourier transformprocessing on received quadrature baseband signal 1214, and outputs thispost-Fourier-transform signal 1216.

[0142] A channel A channel fluctuation estimation section 1217 haspost-Fourier-transform signal 1216 as input, estimates channelfluctuation of the channel A signal (the OFDM signal transmitted fromantenna 110) based on the channel A channel estimation symbols, andoutputs a channel fluctuation estimation group signal 1218. By thismeans, channel fluctuation between antenna 110 and antenna 1211 isestimated. A channel B channel fluctuation estimation section 1219 haspost-Fourier-transform signal 1216 as input, estimates channelfluctuation of the channel B signal (the OFDM signal transmitted fromantenna 120) based on the channel B channel estimation symbols, andoutputs a channel fluctuation estimation group signal 1220. By thismeans, channel fluctuation between antenna 120 and antenna 1211 isestimated.

[0143] A signal processing section 1221 has post-Fourier-transformsignals 1206 and 1216, channel fluctuation estimation group signals 1208and 1218, and channel fluctuation estimation group signals 1210 and 1220as input, and outputs a channel A received quadrature baseband signalgroup 1222 and channel B received quadrature baseband signal group 1223by performing computation using an inverse matrix of a channelfluctuation matrix with channel fluctuation estimation values 1208,1218, 1210, and 1220 as elements.

[0144] A channel A demodulation section 1224 has channel A receivedquadrature baseband signal group 1222 as input, forms a received digitalsignal 1225 by executing demodulation processing corresponding tomodulation section 102 of transmission unit 1000 (FIG. 10) on thatsignal, and outputs received digital signal 1225. A channel Bdemodulation section 1226 has channel B received quadrature basebandsignal group 1223 as input, forms a received digital signal 1227 byexecuting demodulation processing corresponding to modulation section112 of transmission unit 1000 on that signal, and outputs receiveddigital signal 1227.

[0145] A received field strength estimation section 1228 haspost-Fourier-transform signals 1206 and 1216 as input, finds thereceived field strength of these signals, and outputs received fieldstrength estimation information 1229.

[0146] A channel fluctuation estimation section 1230 has channel Achannel fluctuation estimation signal groups 1208 and 1218, and channelB channel fluctuation estimation signal groups 1210 and 1220, as input,and forms and outputs channel fluctuation estimation information 1231.

[0147]FIG. 13 shows a sample configuration of IDFTs 1001 and 1003provided in transmission unit 1000 in FIG. 10. As IDFT 1001 and IDFT1003 have the same configuration, IDFT 1001 will be described here.

[0148] IDFT 1001 has a transmission power modification section 1307.Transmission power modification section 1307 has a carrier 1 transmitquadrature baseband signal 1301, carrier 2 transmit quadrature basebandsignal 1302, carrier 3 transmit quadrature baseband signal 1303, carrier4 transmit quadrature baseband signal 1304, coefficient 125 found fromreception power, and coefficient 124 found from an eigenvalue as input,and by multiplying carrier transmit quadrature baseband signals 1301through 1304 by coefficients 125 and 124, obtainspost-coefficient-multiplication carrier 1 transmit quadrature basebandsignal 1308, post-coefficient-multiplication carrier 2 transmitquadrature baseband signal 1309, post-coefficient-multiplication carrier3 transmit quadrature baseband signal 1310, andpost-coefficient-multiplication carrier 4 transmit quadrature basebandsignal 1311, and outputs these signals.

[0149] Coefficient 125 found from reception power and coefficient 124found from an eigenvalue in this embodiment are found for each carrier.Then transmission power modification section 1307 modifies thetransmission power on a carrier-by-carrier basis by multiplying therespective corresponding carrier transmit quadrature baseband signals bycoefficients 125 and 124.

[0150] An inverse Fourier transform section (IDFT section) 1312 haspost-coefficient-multiplication carrier 1 transmit quadrature basebandsignal 1308, post-coefficient-multiplication carrier 2 transmitquadrature baseband signal 1309, post-coefficient-multiplication carrier3 transmit quadrature baseband signal 1310, andpost-coefficient-multiplication carrier 4 transmit quadrature basebandsignal 1311 as input, obtains a post-inverse-Fourier-transform signal1313 by executing inverse Fourier transform processing on these signals,and outputs post-inverse-Fourier-transform signal 1313.

[0151] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail. Tosimplify the explanation, the drawings used in Embodiment 1 (FIG. 2 andFIG. 6) will be used again here.

[0152] First, the transmission operation of a base station (transmittingapparatus) will be described. Important operations by transmission unit1000 of the base station apparatus shown in FIG. 10 are, firstly, tocontrol the transmission power of OFDM signals transmitted from antennas110 and 120 independently at antennas 110 and 120, and secondly, tocontrol transmission power on a carrier-by-carrier basis. For thispurpose, transmission unit 1000 performs multiplication by coefficientsin IDFTs 1001 and 1003 in order to modify the transmission power oftransmit quadrature baseband signal groups 103 and 113.

[0153] Details of these operations will be described using FIG. 13. FIG.13 shows the detailed configuration of IDFTs 1001 and 1003 in FIG. 10.Transmit orthogonal baseband groups 103 and 113 in FIG. 1.0 correspondto carrier 1 transmit quadrature baseband signal 1301, carrier 2transmit quadrature baseband signal 1302, carrier 3 transmit quadraturebaseband signal 1303, and carrier 4 transmit quadrature baseband signal1304 in FIG. 13, and there is an quadrature baseband signal for eachsubcarrier.

[0154] Transmission power modification section 1307 modifiestransmission power on a carrier-by-carrier basis by multiplyingrespective corresponding carrier transmit quadrature baseband signals bycoefficients 125 and 124. That is to say, coefficient 125 found fromreception power and eigenvalue 126 comprise coefficients for eachcarrier. The coefficient multiplication method used by transmissionpower modification section 1307 is basically as described in Embodiment1, differing only in that coefficient multiplication is performed on acarrier-by-carrier basis.

[0155] Next, the reception operation of a base station (transmittingapparatus) will be described. In this embodiment, reception unit 200 inFIG. 2 receives field strength estimation information 209 for eachcarrier from a communication terminal (receiving apparatus). Thencoefficients 125 and 126 for each carrier are found by reception powerbased coefficient calculation section 211, and coefficient 124 for eachcarrier is found by eigenvalue based coefficient calculation section214. Thus, coefficients 124, 125, and 126 for each carrier are foundbased on field strength estimation information 209 and channelfluctuation estimation information 210 for each carrier sent from acommunication terminal (receiving apparatus). The coefficientcalculation methods used by reception power based coefficientcalculation section 211 and eigenvalue based coefficient calculationsection 214 are basically as described in Embodiment 1, differing onlyin that coefficients are calculated on a carrier-by-carrier basis.

[0156] Next, the reception operation of a communication terminal(receiving apparatus) will be described. Post-Fourier-transform signals1206 and 1216 output from Fourier transform sections (dft's) 1205 and1215 of reception unit 1200 in FIG. 12 comprise signals for eachcarrier.

[0157] Channel A channel fluctuation estimation section 1207 detectsestimation symbols 1101 in FIG. 11(A) and estimates channel fluctuationon a carrier-by-carrier basis. That is to say, h11(t) in Equation (3) isestimated for each carrier, and output as channel A channel fluctuationestimation signal group 1208. Channel B channel fluctuation estimationsection 1209 detects estimation symbols 1101 in FIG. 11(B) and estimateschannel fluctuation on a carrier-by-carrier basis. That is to say,h12(t) in Equation (3) is estimated for each carrier, and output aschannel B channel fluctuation estimation signal group 1210.

[0158] Channel A channel fluctuation estimation section 1217 detectsestimation symbols 1101 in FIG. 11(A) and estimates channel fluctuationon a carrier-by-carrier basis. That is to say, h21(t) in Equation (3) isestimated for each carrier, and output as channel A channel fluctuationestimation signal group 1218. Channel B channel fluctuation estimationsection 1219 detects estimation symbols 1101 in FIG. 11(B) and estimateschannel fluctuation on a carrier-by-carrier basis. That is to say,h22(t) in Equation (3) is estimated for each carrier, and output aschannel B channel fluctuation estimation signal group 1219.

[0159] Received field strength estimation section 1228 haspost-Fourier-transform signals 1206 and 1216 as input, finds thereceived field strength on a carrier-by-carrier basis, and outputsreceived field strength estimation signal 1229.

[0160] Channel fluctuation estimation section 1230 has channelfluctuation estimation signal groups 1208 and 1218, and channelfluctuation estimation signal groups 1210 and 1220, as input, generateschannel fluctuation estimation information for each carrier, and outputsthis as channel fluctuation estimation information 1231.

[0161] Per-carrier received field strength estimation information andper-carrier channel fluctuation estimation information formed in thisway is sent to the base station as feedback information by atransmission unit 500 such as shown in FIG. 5. Received field strengthestimation information 425 in FIG. 5 corresponds to received fieldstrength estimation information 1229 in FIG. 12, and channel fluctuationestimation information 427 in FIG. 5 corresponds to channel fluctuationestimation information 1231 in FIG. 12.

[0162] Thus, according to this embodiment, when a multicarrier signal istransmitted from a plurality of antennas, by receiving informationconstituting an effective reception power index such as per-carrierchannel fluctuation information and per-carrier received field strengthinformation from a receiving apparatus as feedback information, andmodifying the reception power of the multicarrier signal transmittedfrom each antenna independently for each antenna and independently foreach carrier based on this information, it is possible to increase on acarrier-by-carrier basis the effective reception power of themulticarrier signal transmitted from each antenna, and to implement atransmitting apparatus that enables multicarrier signal receptionquality to be improved across all carriers.

[0163] In this embodiment, a case has been described in whichtransmission power of each carrier is changed by IDFTs 1001 and 1003,but transmission power need not be modified by IDFTs 1001 and 1003, butmay instead be modified by modulation sections 102 and 112, or radiosections 106 and 116, for example.

[0164] Also, this embodiment has been described taking OFDM as anexample, but the present invention can be similarly implemented for amethod that combines OFDM processing and spreading processing (such asOFDM-CDMA, for example).

[0165] (Embodiment 3)

[0166] In this embodiment, a transmitting apparatus is described thatreceives at a plurality of antennas a plurality of modulated signalstransmitted from a plurality of antennas, selects a receiving antenna,and performs received signal demodulation using only a received signalfrom the selected receiving antenna.

[0167] Specifically, a plurality of antenna received signal combinationsare created, a channel fluctuation matrix is created for eachcombination, channel fluctuation matrix eigenvalues are calculated foreach combination, and antenna received signals of the combination forwhich the eigenvalue minimum power is greatest are selected, and undergodemodulation processing.

[0168]FIG. 14 shows a sample configuration of the reception unit of areceiving apparatus according to this embodiment. Parts in FIG. 14corresponding to those in FIG. 4 are assigned the same codes as in FIG.4 and detailed descriptions of these parts are omitted. Reception unit1400 is provided in a communication terminal, for example. Here, it isassumed that the transmission unit of a base station that performscommunication with a communication terminal equipped with reception unit1400 is configured as shown in FIG. 1, for example, and signalstransmitted from the base station are configured as shown in FIG. 3.

[0169] Reception unit 1400 has three antennas 401, 411, and 1401, andtwo modulated signals (spread signal A and spread signal B) transmittedfrom transmission unit 100 are received by each of antennas 401, 411,and 1401.

[0170] Radio section 1403 of reception unit 1400 has a received signal1402 received by antenna 1401 as input, forms a received quadraturebaseband signal 1404 by executing predetermined radio processing such asdown-conversion and analog-digital conversion on received signal 1402,and outputs this received quadrature baseband signal 1404. A despreadingsection 1405 has received quadrature baseband signal 1404 as input,forms a despread received quadrature baseband signal 1406 by executingdespreading processing using the same spreading code as that used byspreading section 104 and spreading section 114 in FIG. 1 on receivedquadrature baseband signal 1404, and outputs this despread receivedquadrature baseband signal 1406.

[0171] A spread signal A channel fluctuation estimation section 1407 hasdespread received quadrature baseband signal 1406 as input, estimateschannel fluctuation of spread signal A (the spread signal transmittedfrom antenna 110) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 1408. By this means, channelfluctuation between antenna 110 and antenna 1401 is estimated. A spreadsignal B channel fluctuation estimation section 1409 has despreadreceived quadrature baseband signal 1406 as input, estimates channelfluctuation of spread signal B (the spread signal transmitted fromantenna 120) based on the channel estimation symbols, and outputs achannel fluctuation estimation signal 1410. By this means, channelfluctuation between antenna 120 and antenna 1401 is estimated.

[0172] An antenna selection section 1411 has channel A channelfluctuation estimation signals 408, 418, and 1408, channel B channelfluctuation estimation signals 410, 420, and 1410, and despread receivedquadrature baseband signals 406, 416, and 1406 as input, and selectsfrom among these the optimal antenna received signal combination fordemodulation. The selection method will be described later herein.Antenna selection section 1411 outputs selected spread signal A channelfluctuation estimation signals 1412 and 1415, selected spread signal Bchannel fluctuation estimation signals 1413 and 1416, and selecteddespread received quadrature baseband signals 1414 and 1417.

[0173]FIG. 15 shows a sample configuration of antenna selection section1411. Antenna selection section 1411 has an eigenvalue calculationsection 1501 and a signal selection section 1503. Eigenvalue calculationsection 1501 has channel A channel fluctuation estimation signals 408,418, and 1408, and channel B channel fluctuation estimation signals 410,420, and 1410, as input. That is to say, since three antennas areprovided in this embodiment, three sets of channel fluctuation valuesare input. Then combinations of two sets of the three sets of channelfluctuation values are created (in this embodiment, three combinations),a channel fluctuation matrix is created for each of those combinations,and eigenvalues of each channel fluctuation matrix are calculated. Twosets of signals for inverse matrix calculation are then selected basedon the eigenvalue calculation results, and a control signal 1502indicating which two sets have been selected is output.

[0174] Signal selection section 1503 has channel A channel fluctuationestimation signals 408, 418, and 1408, channel B channel fluctuationestimation signals 410, 420, and 1410, despread received quadraturebaseband signals 406, 416, and 1406, and control signal 1502 as input,and outputs selected spread signal A channel fluctuation estimationsignals 1412 and 1415, selected spread signal B channel fluctuationestimation signals 1413 and 1416, and selected despread receivedquadrature baseband signals 1414 and 1417.

[0175] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail.

[0176] The operation of a base station (transmitting apparatus) is thesame as that described in Embodiment 1, transmitting transmit signals inaccordance with the frame configurations shown in FIG. 3.

[0177] A communication terminal (receiving apparatus) receives transmitsignals at three antennas provided on reception unit 1400 in FIG. 14. Aspecial feature here is that the number of antennas is made larger thanthe number of channels transmitted by the transmitting apparatus, andantenna selection is performed. That is to say, antenna selectionsection 1411 selects two signal groups from signal groups 406, 408, and410 obtained by antenna 401, signal groups 416, 418, and 420 obtained byantenna 411, and signal groups 1406, 1408, and 1410 obtained by antenna1401, and performs separation and demodulation using only the selectedsignal groups.

[0178] The signal group selection method at this time will now bedescribed. First, eigenvalue calculation section 1501 shown in FIG. 15creates a channel fluctuation matrix as shown in Equation (3) usingchannel fluctuation estimation signals 408, 410, 418, and 420 in therelationship in FIG. 7, and finds value P1 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1501 also creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 408, 410, 1408, and 1410 in therelationship in FIG. 7, and finds value P2 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1501 further creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 418, 420, 1408, and 1410 in therelationship in FIG. 7, and finds value P3 with the smallest power amongthose eigenvalues.

[0179] Eigenvalue calculation section 1501 then searches for the largestvalue among P1, P2, and P3. If P1 is the largest, eigenvalue calculationsection 1501 outputs a control signal 1502 indicating that signals 408,410, 406, 418, 420, and 416 are to be selected. That is to say,eigenvalue calculation section 1501 instructs signal selection section1503 to select the signal groups obtained from antennas 401 and 411 inFIG. 14.

[0180] At this time, signal selection section 1503 outputs signal 408 assignal 1412, signal 410 as signal 1413, signal 406 as signal 1414,signal 418 as signal 1415, signal 420 as signal 1416, and signal 416 assignal 1417. Similarly, if P2 is the largest the signal groups obtainedfrom antennas 401 and 1401 are selected, and if P3 is the largest thesignal groups obtained from antennas 411 and 1401 are selected.

[0181] Signal processing section 421 in FIG. 14 sets up Equation (3) inthe relationship in FIG. 7 using input signals 1412, 1413, 1414, 1415,1416, and 1417, and by performing the inverse matrix operation of thatequation, separates the signals of each channel and outputs separatedchannel signals 422 and 423.

[0182] By switching receiving antennas based on the channel fluctuationmatrix eigenvalue for which power is smallest in this way, it ispossible to select the antenna with the best reception quality. By thismeans, the error rate characteristics of demodulated data can beimproved.

[0183] Eigenvalue minimum power corresponds to the effective receptionpower of a modulated signal contained in an antenna received signal usedto obtain that eigenvalue, and therefore selecting an antenna receivedsignal for which eigenvalue minimum power is greatest is equivalent toselecting an antenna received signal combination for which modulatedsignal effective reception power is greatest. It is therefore possibleto demodulate each modulated signal using a combination of antennareceived signals for which modulated signal effective reception power isgreatest, enabling modulated signal demodulation precision to be greatlyimproved compared with the case where each modulated signal isdemodulated using all antenna received signals.

[0184] Thus, according to this embodiment, by creating a plurality ofantenna received signal combinations, creating a channel fluctuationmatrix for each combination, calculating channel fluctuation matrixeigenvalues for each combination, selecting antenna received signals ofthe combination for which the eigenvalue minimum power is greatest, andperforming demodulation processing, it is possible to implement areceiving apparatus that enables the error rate characteristics of areceived plurality of channel signals to be improved.

[0185] In this embodiment a case has been described in which modulatedsignals of two channels transmitted from two antennas are received bythree antennas, but the number of transmitting antennas and number ofreceiving antennas are not limited to these numbers. The presentinvention can be widely applied to cases where a plurality oftransmitting antennas are provided, a greater number of receivingantennas are provided, and receiving antennas equal to the number ofchannels are selected from the plurality of receiving antenna signals.

[0186] Also, in the above-described embodiment, a spread spectrumcommunication system has been described by way of example, but this isnot a limitation, and the present invention can be similarly implementedin a single-carrier system that does not have a spreading section, or anOFDM system, for example. A case in which the present invention isapplied to an OFDM system is described in detail in Embodiment 4.

[0187] (Embodiment 4)

[0188] In this embodiment, a case is described in which the processingdescribed in Embodiment 3 is applied to OFDM communications. A specialfeature of this embodiment is that the following processing is performedfor each subcarrier: a plurality of antenna received signal combinationsare created, a channel fluctuation matrix is created for eachcombination, channel fluctuation matrix eigenvalues are calculated foreach combination, and antenna received signals of the combination forwhich the eigenvalue minimum power is greatest are selected, and undergodemodulation processing.

[0189]FIG. 16 shows a sample configuration of the reception unit of areceiving apparatus according to this embodiment. Reception unit 1600 ofthis embodiment has many parts combining Embodiment 2 and Embodiment 3,and therefore parts corresponding to parts in FIG. 12 described inEmbodiment 2 are assigned the same codes as in FIG. 12, partscorresponding to parts in FIG. 14 described in Embodiment 3 are assignedthe same codes as in FIG. 14, and descriptions of these parts areomitted.

[0190] Reception unit 1600 is provided in a communication terminal, forexample. Here, it is assumed that the transmission unit of a basestation that performs communication with a communication terminalequipped with reception unit 1600 is configured as shown in FIG. 10, forexample, and signals transmitted from the base station are configured asshown in FIG. 11.

[0191] Reception unit 1600 has three antennas 401, 411, and 1401, andtwo OFDM signals transmitted from transmission unit 1000 are received byeach of antennas 401, 411, and 1401. A special feature of reception unit1600 here is that the number of antennas (in this embodiment three) isgreater than the number of channels of signals transmitted bytransmission unit 1000 (in this embodiment, two).

[0192] Received signals 402, 412, and 1402 of antennas 401, 411, and1401 become received quadrature baseband signals 404, 414, and 1404 byundergoing predetermined radio processing such as down-conversion andanalog-digital conversion by radio sections 403, 413, and 1403,respectively. Received quadrature baseband signals 404, 414, and 1404become post-Fourier-transform signals 1206, 1216, and 1602 by undergoingFourier transform processing by Fourier transform sections (dft's) 1205,1215, and 1601, respectively.

[0193] Post-Fourier-transform signals 1206,1216, and 1602 obtained foreach antenna are sent to channel A channel fluctuation estimationsections 1207, 1217, and 1603, and channel B channel fluctuationestimation sections 1209, 1219, and 1605, provided for each antenna.Channel A channel fluctuation estimation sections 1207, 1217, and 1603obtain per-carrier channel fluctuation estimation signal groups 1208,1218, and 1604 for channel A, and send these to a signal processingsection 1607.

[0194] Signal processing section 1607 performs processing combiningantenna selection section 1411 and signal processing section 421 in FIG.14. That is to say, signal processing section 1607 performs antennasignal selection based on eigenvalue power, and also performs channelsignal separation processing using the selected antenna signals.However, signal processing section 1607 of this embodiment differs fromreception unit 1400 in FIG. 14 in that the above antenna signalselection processing and channel signal separation processing areperformed on a carrier-by-carrier basis. Signal processing section 1607has channel A channel fluctuation estimation signal groups 1208, 1218,and 1604, channel B channel fluctuation estimation signal groups 1210,1220, and 1606, and post-Fourier-transform signals 1206, 1216, and 1602as input, and outputs a channel A received quadrature baseband signal1608 and channel B received quadrature baseband signal 1609 on whichselection processing and separation processing have been executed on acarrier-by-carrier basis.

[0195]FIG. 17 shows the detailed configuration of signal processingsection 1607. The signal processing section configuration shown in FIG.17 is the configuration for performing processing for one carrier, andsignal processing section 1607 in FIG. 16 is actually provided with acircuit as shown in FIG. 17 for each carrier.

[0196] Eigenvalue calculation section 1701 has the same function aseigenvalue calculation section 1501 in FIG. 15 described in Embodiment3. That is to say, eigenvalue calculation section 1701 creates a channelfluctuation matrix as shown in Equation (3) using channel fluctuationestimation signals 1208-1, 1210-1, 1218-1, and 1220-1 for carrier 1 inFIG. 11 from among channel fluctuation estimation signal groups 1208,1210, 1218, and 1220, and finds value P1 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1701 also creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 1208-1, 1210-1, 1604-1, and 1606-1 forcarrier 1 from among channel fluctuation estimation signal groups 1208,1210, 1604, and 1606, and finds value P2 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1701 further creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 1218-1, 1220-1, 1604-1, and 1606-1 forcarrier 1 from among channel fluctuation estimation signal groups 1218,1220, 1604, and 1606, and finds value P3 with the smallest power amongthose eigenvalues.

[0197] Eigenvalue calculation section 1701 then searches for the largestvalue among P1, P2, and P3. If P1 is the largest, eigenvalue calculationsection 1701 outputs a control signal 1702 indicating that signals1208-1, 1210-1, 1206-1, 1218-1, 1220-1, and 1216-1 are to be selected.That is to say, eigenvalue calculation section 1701 instructs signalselection section 1703 to select the signal groups obtained fromantennas 401 and 411 in FIG. 16.

[0198] At this time, signal selection section 1703 outputs signal 1208-1as signal 1704, signal 1210-1 as signal 1705, signal 1206-1 as signal1706, signal 1218-1 as signal 1707, signal 1220-1 as signal 1708, andsignal 1216-1 as signal 1709. Similarly, if P2 is the largest the signalgroups obtained from antennas 401 and 1401 are selected, and if P3 isthe largest the signal groups obtained from antennas 411 and 1401 areselected.

[0199] A computation section 1710 sets up Equation (3) in therelationship in FIG. 7 using input signals 1704 through 1709, and byperforming the inverse matrix operation of that equation, separates thesignals of each channel and outputs separated channel A carrier 1quadrature baseband signal 1608-1 and channel B carrier 1 quadraturebaseband signal 1609-1.

[0200] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail.

[0201] The operation of a base station (transmitting apparatus) is thesame as that described in Embodiment 2, transmitting transmit signals inaccordance with the frame configurations shown in FIG. 11.

[0202] A communication terminal (receiving apparatus) receives twochannels of OFDM signals at three antennas provided on reception unit1600 in FIG. 16. Reception unit 1600 then estimates channel fluctuationon a channel-by-channel basis and on a carrier-by-carrier basis forreception at each antenna.

[0203] Reception unit 1600 then performs the following processing foreach carrier: creation of a plurality of antenna received signalcombinations, creation of a channel fluctuation matrix for eachcombination, channel fluctuation matrix eigenvalue calculation for eachcombination, and selection of antenna received signals of thecombination for which the eigenvalue minimum power is greatest. In thisembodiment, as the number of received OFDM signal channels is two andthe number of receiving antennas is three, three combinations arecreated, and one combination is selected from among these threecombinations.

[0204] Next, reception unit 1600 separates the signals of each channelmultiplexed on the propagation path by performing an inverse matrixoperation using the selected combination of antenna received signals(channel fluctuation estimation and quadrature baseband signals) Then,lastly, receive data is obtained by demodulating the separated channelsignals.

[0205] As reception unit 1600 selects an antenna received signal forwhich channel fluctuation matrix eigenvalue minimum power is greatest,separates modulated signals (that is, signals transmitted from differentantennas) multiplexed on the propagation path using the selected antennareceived signal, and performs demodulation processing in this way on acarrier-by-carrier basis, it is possible to perform signal separationand demodulation processing using the antenna received signal with thegreatest effective reception power.

[0206] With OFDM signals in particular, effective reception powerdiffers greatly from carrier to carrier due to the effects of frequencyselective fading, etc. In this embodiment this is taken intoconsideration, and the optimal antenna received signal combination isselected on a carrier-by-carrier basis by performing antenna selectionbased on eigenvalues for each carrier. By this means, error ratecharacteristics can be improved across all carriers.

[0207] Thus, according to this embodiment, by performing, on acarrier-by-carrier basis, creation of a plurality of antenna receivedsignal combinations, creation of a channel fluctuation matrix for eachcombination, channel fluctuation matrix eigenvalue calculation for eachcombination, selection of antenna received signals of the combinationfor which the eigenvalue minimum power is greatest, and demodulationprocessing, it is possible to implement a receiving apparatus thatenables the error rate characteristics of received OFDM signals of aplurality of channels to be improved across all carriers.

[0208] In this embodiment a case has been described in which OFDMsignals of two channels transmitted from two antennas are received bythree antennas, but the number of transmitting antennas and number ofreceiving antennas are not limited to these numbers. The presentinvention can be widely applied to cases where a plurality oftransmitting antennas are provided, a greater number of receivingantennas are provided, and receiving antennas equal to the number ofchannels are selected from the plurality of receiving antenna signals.

[0209] Also, in this embodiment, an OFDM system has been described byway of example, but the present invention can be similarly implementedin a system combining an spread spectrum system as described inEmbodiment 3 and an OFDM system, and can also be similarly implementedin a multicarrier system other than OFDM.

[0210] (Embodiment 5)

[0211] In this embodiment, a receiving apparatus is described thatreceives at a plurality of antennas a plurality of modulated signalstransmitted from a plurality of antennas, and performs weighting andcombining of received signals received at each receiving antenna basedon channel fluctuation matrix eigenvalues.

[0212] To be specific, firstly, a plurality of antenna received signalcombinations are created, a channel fluctuation matrix is created foreach combination, and channel fluctuation matrix eigenvalues arecalculated for each combination. Then, modulated signals are separatedusing the antenna received signals of each combination and the channelfluctuation matrix corresponding to that combination, and modulatedsignals separated in each combination are weighted and combined usingthe channel fluctuation estimation matrix eigenvalues used at the timeof separation.

[0213]FIG. 18 shows a sample configuration of the reception unit of areceiving apparatus according to this embodiment. Parts in FIG. 18corresponding to parts in FIG. 14 are assigned the same codes as in FIG.14, and descriptions of these parts are omitted. Reception unit 1800 isprovided in a communication terminal, for example. Here, it is assumedthat the transmission unit of a base station that performs communicationwith a communication terminal equipped with reception unit 1800 isconfigured as shown in FIG. 1, for example, and signals transmitted fromthe base station are configured as shown in FIG. 3.

[0214] The difference between reception unit 1400 in FIG. 14 describedin Embodiment 3 and reception unit 1800 of this embodiment is that,whereas reception unit 1400 selects an antenna signal using separationand demodulation based on channel fluctuation matrix eigenvalues,reception unit 1800 of this embodiment weights and combines antennareceived signals based on channel fluctuation matrix eigenvalues.Therefore, reception unit 1800 has a signal processing section 1801instead of antenna selection section 1411 and signal processing section421 of reception unit 1400, and performs weighting and combiningprocessing on antenna received signals based on channel fluctuationmatrix eigenvalues by means of signal processing section 1801.

[0215] That is to say, signal processing section 1801 has three sets ofantenna signals—spread signal A channel fluctuation estimation signals408, 418, and 1408, spread signal B channel fluctuation estimationsignals 410, 420, and 1410, and despread received quadrature basebandsignals 406,416, and 1406—as input, creates combinations each of twosets of signals in the same way as in Embodiment 3, creates a channelfluctuation matrix for each combination, and calculates the eigenvaluethereof for each combination. Signal processing section 1801 alsoseparates channel A and channel B signals for each combination byperforming channel fluctuation matrix inverse matrix computations foreach combination. The channel signals separated on acombination-by-combination basis then undergo weighting and combiningusing the eigenvalues corresponding to each combination. Signalprocessing section 1801 then outputs weighted and combined channelsignals 422 and 423.

[0216]FIG. 19 shows a sample configuration of signal processing section1801. Signal processing section 1801 has an eigenvalue calculationsection 1901 and a separation/combination section 1903. Eigenvaluecalculation section 1901 has spread signal A channel fluctuationestimation signals 408, 418, and 1408, and spread signal B channelfluctuation estimation signals 410, 420, and 1410, as input. That is tosay, since three antennas are provided in this embodiment, three sets ofchannel fluctuation values are input. Then combinations of two sets ofthe three sets of channel fluctuation values are created (in thisembodiment, three combinations), a channel fluctuation matrix is createdfor each of those combinations, and eigenvalues of each channelfluctuation matrix are calculated. Eigenvalues for each combination arethen output as an eigenvalue estimation signal 1902.

[0217] Separation/combination section 1903 has spread signal A channelfluctuation estimation signals 408, 418, and 1408, spread signal Bchannel fluctuation estimation signals 410, 420, and 1410, despreadreceived quadrature baseband signals 406, 416, and 1406, and eigenvalueestimation signal 1902 as input, performs channel signal separationprocessing on a combination-by-combination basis, and also performsweighting and combining processing on the antenna received signals usingeigenvalue estimation signal 1902. By this means, separation/combinationsection 1903 obtains spread signal A received quadrature baseband signal422 and spread signal B received quadrature baseband signal 423, whichit outputs.

[0218] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail.

[0219] The operation of a base station (transmitting apparatus) is thesame as that described in Embodiment 1, transmitting transmit signals inaccordance with the frame configurations shown in FIG. 3.

[0220] A communication terminal (receiving apparatus) receives transmitsignals at three antennas provided on reception unit 1800 in FIG. 18.Reception unit 1800 then estimates channel fluctuation on achannel-by-channel basis for reception at each antenna by means ofchannel fluctuation estimation sections 407, 409, 417, 419, 1407, and1409.

[0221] Next, reception unit 1800 creates a plurality of antenna receivedsignal combinations, forms a channel fluctuation matrix for eachcombination, and calculates channel fluctuation matrix eigenvalues foreach combination. Reception unit 1800 performs this per-combinationeigenvalue calculation processing by means of eigenvalue calculationsection 1901.

[0222] Specifically, eigenvalue calculation section 1901 creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 408, 410, 418, and 420 in therelationship in FIG. 7, and finds value P1 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1901 also creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 408, 410, 1408, and 1410 in therelationship in FIG. 7, and finds value P2 with the smallest power amongthose eigenvalues. Eigenvalue calculation section 1901 further creates achannel fluctuation matrix as shown in Equation (3) using channelfluctuation estimation signals 418, 420, 1408, and 1410 in therelationship in FIG. 7, and finds value P3 with the smallest power amongthose eigenvalues. Then eigenvalue calculation section 1901 sendsobtained values P1, P2, and P3 to separation/combination section 1903 asan eigenvalue estimation signal 1902.

[0223] Separation/combination section 1903 first performs channel signalseparation processing for each antenna received signal combination. Inthis embodiment, separation processing is performed for three sets ofantenna received signals. That is to say, for the first set,separation/combination section 1903 sets up Equation (3) in therelationship in FIG. 7 using input signals 408, 410, 406, 418, 420, and416, and performs the inverse matrix operation of that equation. Thespread signal A received quadrature baseband signal and spread signal Breceived quadrature baseband signal thus obtained are designated Ra1 andRb1 respectively. For the second set, separation/combination section1903 sets up Equation (3) in the relationship in FIG. 7 using inputsignals 408, 410, 406, 1408, 1410, and 1406, and performs the inversematrix operation of that equation. The spread signal A receivedquadrature baseband signal and spread signal B received quadraturebaseband signal thus obtained are designated Ra2 and Rb2 respectively.For the third set, separation/combination section 1903 sets up Equation(3) in the relationship in FIG. 7 using input signals 418, 420, 416,1408, 1410, and 1406, and performs the inverse matrix operation of thatequation. The spread signal A received quadrature baseband signal andspread signal B received quadrature baseband signal thus obtained aredesignated Ra3 and Rb3 respectively.

[0224] Separation/combination section 1903 performs the weighting andcombining operations of the following equations using the thus obtainedsets of received quadrature baseband signals Ra1, Rb1, Ra2, Rb2, Ra3,and Rb3, and eigenvalues P1, P2, and P3 corresponding to each set,thereby obtaining weighted and combined spread signal A receivedquadrature baseband signal Ra (422) and spread signal B receivedquadrature baseband signal Rb (423).

[0225] [Equations 4] $\begin{matrix}{{{Ra} = {\frac{1}{3\left( {{P1} + {P2} + {P3}} \right)}\left( {{{P1} \times {Ra1}} + {{P2} \times {Ra2}} + {{P3} \times {Ra3}}} \right)}}{{Rb} = {\frac{1}{3\left( {{P1} + {P2} + {P3}} \right)}\left( {{{P1} \times {Rb1}} + {{P2} \times {Rb2}} + {{P3} \times {Rb3}}} \right)}}} & (4)\end{matrix}$

[0226] By thus performing weighting to find the received quadraturebaseband signal of each channel, more precise spread signal A and Breceived quadrature baseband signals 422 and 423 are obtained. This isbecause eigenvalue power is a value corresponding to effective receptionpower. Thus, in reception processing of this embodiment, effective useis made of reception levels using channel fluctuation matrix eigenvaluepower—that is to say, effective reception levels are found and signalcombination is performed based on these effective reception levels.

[0227] Spread signal A and B received quadrature baseband signals 422and 423 output from separation/combination section 1903 each undergoorthogonal demodulation processing by a demodulation section (not shown)to become receive data. As a result, it is possible to obtain receivedata of each channel with good error rate characteristics.

[0228] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas a plurality of modulated signalstransmitted from a plurality of antennas, by weighting and combiningreceived signals obtained at each receiving antenna based on channelfluctuation matrix eigenvalues it is possible to weight more heavily anantenna received signal with greater effective reception power, enablingthe error rate characteristics of a received plurality of channelsignals to be improved.

[0229] In this embodiment a case has been described in which modulatedsignals of two channels transmitted from two antennas are received bythree antennas, but the number of transmitting antennas and number ofreceiving antennas are not limited to these numbers. The presentinvention can be widely applied to cases where a plurality oftransmitting antennas are provided, a greater number of receivingantennas are provided, and receiving antennas equal to the number ofchannels are selected from the plurality of receiving antenna signals.

[0230] Also, in this embodiment a method has been described wherebychannel fluctuation matrix eigenvalue power is taken as a weightingcoefficient, and received quadrature baseband signal weighting andcombining is performed based on this coefficient, but the presentinvention is not limited to this.

[0231] The method according to the present embodiment can be applied tocases where received signals are applied error correction codes such asconvolutional code, turbo code, and low density parity code. Thedecoding in this case is executed by finding a branch metric and a pathmetric sequentially based on weighted results.

[0232] For example, channel fluctuation matrix eigenvalue powerdescribed in this embodiment may also be used as a weighting coefficientfor MLD (Maximum Likelihood Detection) shown in “A simple transmitdiversity technique for wireless communications” IEEE Journal on SelectAreas in Communications, vol. 16, no. 8, October 1998. Use of channelfluctuation matrix eigenvalue power as a weighting coefficient indemodulation and decoding when performing MLD improves receptionquality. A weighting method using an eigenvalue for MLD is described indetail in Embodiment 7 onward.

[0233] (Embodiment 6)

[0234] In this embodiment, a case is described in which the processingdescribed in Embodiment 5 is applied to OFDM communications. A specialfeature of this embodiment is that the processing described inEmbodiment 5 whereby received signals obtained at each receiving antennaare weighted and combined based on channel fluctuation matrixeigenvalues is performed for each carrier.

[0235]FIG. 18 and FIG. 19 used in Embodiment 5 will also be used indescribing this embodiment. The reception unit of this embodiment has aconfiguration in which despreading sections 405, 415, and 1405 in FIG.18 are replaced by Fourier transform sections (dft's), channelfluctuation estimation sections 407, 409, 417, 419, 1407, and 1409 inFIG. 18 are configured so as to estimate signal channel fluctuation on acarrier-by-carrier basis, and signal processing section 1801 in FIG. 18is configured so as to weight and combine antenna received signals ofeach carrier using per-carrier channel fluctuation matrix eigenvalues asweight coefficients.

[0236] Actually, the kind of configuration shown in FIG. 19 is providedfor each carrier as a signal processing section, and the channelfluctuation matrix eigenvalue based weighting and combining described inEmbodiment 5 is performed for each carrier. As a result, the signalerror rate characteristics can be improved for all carriers.

[0237] As also described in Embodiment 4, with OFDM signals, effectivereception power differs greatly from carrier to carrier due to theeffects of frequency selective fading, etc. In this embodiment this istaken into consideration, and the weight coefficient used in combiningis changed on a carrier-by-carrier basis by performing signal combiningwith eigenvalue power as a weight coefficient on a carrier-by-carrierbasis. By this means, error rate characteristics can be improved acrossall carriers.

[0238] Thus, according to-this embodiment, when OFDM signals transmittedfrom a plurality of antennas are received at a plurality of antennas anddemodulated, by performing processing whereby received signals obtainedat each receiving antenna are weighted and combined based on channelfluctuation matrix eigenvalues, as described in Embodiment 5, for eachcarrier, it is possible to implement a receiving apparatus that enablesthe error rate characteristics of received OFDM signals of a pluralityof channels to be improved across all carriers.

[0239] In this embodiment a method has been described whereby receivedquadrature baseband signal weighting and combining is performed on acarrier-by-carrier basis using channel fluctuation matrix eigenvaluepower as a weighting coefficient, but the present invention is notlimited to this.

[0240] For example, channel fluctuation matrix eigenvalue powerdescribed in this embodiment may also be used as a weighting coefficientfor MLD (Maximum Likelihood Detection) shown in “A simple transmitdiversity technique for wireless communications” IEEE Journal on SelectAreas in Communications, vol. 16, no. 8, October 1998. Use ofper-carrier channel fluctuation matrix eigenvalue power as a per-carrierweighting coefficient in demodulation and decoding improves receptionquality. MLD is described in detail in Embodiment 9 and Embodiment 10.

[0241] (Embodiment 7)

[0242] In this embodiment, a receiving apparatus is described thatreceives at a plurality of antennas a plurality of modulated signalstransmitted from a plurality of antennas, and performs weightingprocessing on received signals and demodulates received signals usingchannel fluctuation matrix eigenvalues and the received field strengthof each antenna received signal.

[0243] Specifically, a soft decision value of each modulated signalafter separation is weighted using a channel fluctuation matrixeigenvalue. By this means, a soft decision value can be given anappropriate likelihood according to the effective reception power of themodulated signal. As a result, the error rate characteristics of areceived digital signal obtained by a decoding section is improved.

[0244] First, the configuration of a transmitting apparatus will bedescribed. FIG. 20 shows an example of the configuration of thetransmission unit of a transmitting apparatus according to thisembodiment. The difference between transmission unit 2000 of thisembodiment and transmission unit 100 in FIG. 1 is that transmission unit2000 has error correction coding sections 2001 and 2002. The rest of theconfiguration is the same as that of transmission unit 100 in FIG. 1,and therefore a description thereof is omitted here.

[0245] Error correction coding sections 2001 and 2002 have transmitdigital signals 101 and 111 as input respectively, obtain errorcorrection coded signals 2003 and 2004 by executing error correctioncoding processing on transmit digital signals 101 and 111 usingconvolutional code, and output these signals 2003 and 2004.

[0246] Modulation sections 102 and 112 have error correction codedsignals 2003 and 2004 as input respectively, and executed modulationprocessing on error correction coded signals 2003 and 2004. In thisembodiment, a case is described in which modulation sections 102 and 112execute BPSK modulation as shown in FIG. 22, but other modulationprocessing such as QPSK or 16QAM may also be executed.

[0247] Transmission unit 2000 is provided in a base station, forexample, which has a reception unit 200 as shown in FIG. 2. Transmissionunit 2000 transmits signals with the frame configurations shown in FIG.3.

[0248] Next, the configuration of a receiving apparatus will bedescribed. FIG. 21 shows the configuration of a reception unit of thisembodiment that receives signals transmitted from transmission unit2000. Reception unit 2100 is provided in a communication terminal, forexample. The difference between reception unit 2100 of this embodimentand reception unit 400 in FIG. 4 is that reception unit 2100 has aneigenvalue based coefficient calculation section 2101, soft decisionvalue calculation sections 2102 and 2104, error correction decodingsections 2103 and 2105, and reception level based coefficientcalculation section 2106. The rest of the configuration is the same asthat of reception unit 400 in FIG. 4, and therefore a descriptionthereof is omitted here.

[0249] Eigenvalue based coefficient calculation section 2101 has channelfluctuation estimation information 427 as input, and outputs acoefficient 2110 found from an eigenvalue. Specifically, as alsodescribed in Embodiment 1, channel fluctuation h11(t), h12(t), h21(t),and h22(t) estimates are input as channel fluctuation estimationinformation 427, Equation (3) channel fluctuation matrix eigenvaluecalculation is performed with these estimates as elements, andcoefficient 2110 is found based on the value with the smallest poweramong the eigenvalue powers. That is to say, coefficient 2110 is foundby performing the same calculation as performed by eigenvalue basedcoefficient calculation section 214 (FIG. 2) described in Embodiment 1,and this coefficient 2110 is sent to soft decision value calculationsections 2102 and 2104.

[0250] Reception level based coefficient calculation section 2106 hasreceived quadrature baseband signals 406 and 416 as input, calculatescoefficients 2115 and 2116 based on received quadrature baseband signals406 and 416, and sends these coefficients 2115 and 2116 to soft decisionvalue calculation sections 2102 and 2104 respectively. Specifically,spread signal A reception level based coefficient 2115 is found based onthe reception level of the despread signal (received quadrature basebandsignal) for spread signal A obtained by despreading section 405 and 415respectively, and this coefficient 2115 is sent to soft decision valuecalculation section 2102. Similarly, spread signal B reception levelbased coefficient 2116 is found based on the reception level of thedespread signal (received quadrature baseband signal) for spread signalB obtained by despreading section 405 and 415 respectively, and thiscoefficient 2116 is sent to soft decision value calculation section2104.

[0251] Soft decision value calculation section 2102 has spread signal Areceived quadrature baseband signal 422, coefficient 2115 found from thereception levels, and coefficient 2110 found from the eigenvalues asinput, obtains a soft decision value by multiplying spread signal Areceived quadrature baseband signal 422 by coefficients 2115 and 2110,and outputs this soft decision value as soft decision value signal 2111.Error correction decoding section 2103 has soft decision value signal2111 as input, and obtains and outputs received digital signal 2112 thathas been error correction decoded by executing error correction decodingprocessing on soft decision value signal 2111.

[0252] Soft decision value calculation section 2104 has spread signal Breceived quadrature baseband signal 423, coefficient 2116 found from thereception levels, and coefficient 2110 found from the eigenvalues asinput, obtains a soft decision value by multiplying spread signal Breceived quadrature baseband signal 423 by coefficients 2116 and 2110,and outputs this soft decision value as soft decision value signal 2113.Error correction decoding section 2105 has soft decision value signal2113 as input, and obtains and outputs received digital signal 2114 thathas been error correction decoded by executing error correction decodingprocessing on soft decision value signal 2113.

[0253] It is assumed that a receiving apparatus (communication terminal)according to this embodiment has a transmission unit 500 as shown inFIG. 5 in addition to reception unit 2100 shown in FIG. 21, andtransmits signals with the frame configuration shown in FIG. 6 fromtransmission unit 500.

[0254] The operation of a transmitting apparatus and receiving apparatusaccording to this embodiment will now be described in detail. In thisembodiment the receiving apparatus has special features, and thereforethe operation of the receiving apparatus will be described in particulardetail. The description will focus on operations differing from those inEmbodiment 1, omitting operations that are the same as those inEmbodiment 1.

[0255] Reception unit 2100 executes radio signal processing, despreadingprocessing, channel fluctuation estimation processing for each spreadsignal, and so forth, on signals received at antennas 401 and 402, thenperforms Equation (3) inverse matrix computation in signal processingsection 421, and obtains spread signal A received quadrature basebandsignal 422 and spread signal B received quadrature baseband signal 423.

[0256] It is here assumed that reception unit 2100 receives a BPSKmodulated signal with a signal point arrangement as shown in FIG. 22.When coordinates of two points in the IQ plane are normalized by(+1.0,0.0) and (−1.0,0.0) in BPSK modulation, the soft decision value ofreceived quadrature baseband signal R′(t) in the example shown in FIG.22 is +0.6 as shown in FIG. 23.

[0257] Important points concerning operation in this embodiment are thatweighting is performed in soft decision value calculation sections 2102and 2104 on a soft decision value obtained from a received quadraturebaseband signal as described above, and more particularly that weightingis performed using coefficients found from eigenvalues.

[0258] To be specific, firstly, matrix eigenvalues shown in Equation (3)are found by eigenvalue based coefficient calculation section 2101 usingchannel fluctuation estimation information 427—that is, estimatedh11(t), h12(t), h21(t), and h22(t)—generated by channel fluctuationinformation generation section 426, and coefficient D(t) 2110 iscalculated from the value with the smallest power among the eigenvalues.

[0259] On the other hand, in reception level based coefficientcalculation section 2106, reception level based coefficients Ca(t) 2115and Cb(t) 2116 are obtained from the R1(t) and R2(t) reception levels(in this embodiment, R1(t) and R2(t) are despread signals).

[0260] Using coefficients D(t) and Ca(t) obtained as described above andreceived quadrature baseband signal R′a(t) 422, received signal softdecision value Sa(t) 2111 is calculated by soft decision valuecalculation section 2102 using the following equation.

[0261] [Equation 5]

S _(a)(t)=C _(a)(t)×D(t)×R′ _(a)(t)   (5)

[0262] Similarly, using coefficients D(t) and Cb(t) obtained asdescribed above and received quadrature baseband signal R′b(t) 423,received signal soft decision value Sb(t) 2113 is calculated by softdecision value calculation section 2104 using the following equation.

[0263] [Equation 6]

S _(b)(t)=C _(b)(t)×D(t)×R′ _(b)(t)   (6)

[0264] In error correction decoding section 2103, error correctiondecoding processing is performed using soft decision value Sa(t) 2111obtained as described above. Similarly, in error correction decodingsection 2105, error correction decoding processing is performed usingsoft decision value Sb(t) 2113 obtained as described above.

[0265] Here, coefficients Ca(t)×D(t) and Cb(t)×D(t) for weighting usedby soft decision value calculation sections 2102 and 2104 indicate theeffective received field strength obtained by multiplying the receivedfield strength actually received by an efficiency coefficient.Performing multiplication by this coefficient enables receptioncharacteristics to be improved.

[0266] In this embodiment, convolutional coding is executed as errorcorrection coding, and therefore maximum likelihood decoding such asViterbi decoding is used. As regards the way in which a soft decisionvalue is used in maximum likelihood decoding, methods previouslydisclosed in various documents include, for example, a method wherebythe Euclidian distance between a soft decision value and each signalpoint is calculated and used, and a method whereby a metric value iscalculated based on probability density distribution characteristics. Inthis embodiment, it is assumed, as an example, that the square Euclidiandistance is calculated. That is to say, in the example shown in FIG. 23,likelihood metric values M0 and M1 from each signal point are calculatedas shown in following Equation (7) and Equation (8) respectively. Bythis means, received digital signals 2112 and 2113 decoded by Viterbicoding are obtained.

[0267] [Equation 7]

M ₀(t)=(+0.6−(−1.0))²=2.56   (7)

[0268] [Equation 8]

M ₁(t)=(+0.6−(+1.0))²=0.16   (8)

[0269] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas a plurality of modulated signalstransmitted from a plurality of antennas, by weighting a soft decisionvalue using a coefficient D(t) based on the minimum value of eigenvaluescalculated from channel fluctuation estimation results when performingerror correction decoding using a received baseband signal obtained byseparation, it is possible to give a soft decision value an appropriatelikelihood based on effective reception power, enabling receive dataerror rate characteristics to be improved.

[0270] In this embodiment, in calculating reception level basedcoefficients, reception level based coefficient calculation section 2106(FIG. 21) finds spread signal A reception level based coefficient 2115and spread signal B reception level based coefficient 2116 based on theoutput from despreading sections 405 and 415, but coefficients 2115 and2116 may also be found using channel estimation information h11(t),h12(t), h21(t), and h22(t) obtained by channel fluctuation estimationsections 407, 409, 417, and 419, in the same way as with reception powerbased coefficient calculation section 211 in FIG. 2 described inEmbodiment 1, or may be found from the RSSI (Received Signal StrengthIndicator) of the received signal received from each antenna. This alsoapplies to other embodiments in which processing is performed that usesreception level based coefficients.

[0271] Also, in this embodiment a case has been described in which softdecision value weighting is performed using reception level basedcoefficients 2115 and 2116 in addition to eigenvalue based coefficient2110, but soft decision value weighting may also be performed using onlyan eigenvalue based coefficient.

[0272] Moreover, the configuration of the transmission unit of a basestation is not limited to that shown in FIG. 20. For example,transmission power modification sections 108 and 118 are not essential,and a configuration may be used whereby modulated signals 107 and 117are supplied directly to antennas 110 and 120.

[0273] Furthermore, a function that performs error detection coding, aninterleaving function that switches around the signal order, apuncturing function that reduces redundancy by eliminating some signals,or the like, may be provided before or after error correction codingsections 2001 and 2002, as necessary, without affecting the presentinvention. This also applies to other embodiments that have errorcorrection coding sections.

[0274] Also, in this embodiment a case has been described in which errorcorrection coding sections 2001 and 2002 perform error correction codingprocessing using convolutional code, but the error correction code usedin error correction coding processing is not limited to convolutionalcode, and other code may be used as long as it is error correction codethat allows decoding processing using a soft decision value duringdecoding. In this case, error correction decoding sections 2103 and 2105of reception unit 2100 should perform decoding processing correspondingto the relevant coding. Moreover, a configuration may be used in whicherror correction coding sections 2001 and 2002 are combined into asingle error correction coding section, and a coded signal is separatedinto two signals that are supplied to modulation section 102 andmodulation section 112 respectively. In this case, error correctiondecoding sections 2103 and 2105 of reception unit 2100 can also becombined into a single decoding processing section. These comments alsoapply to other embodiments that have error correction coding processingsections.

[0275] Furthermore, in this embodiment a reception unit 2100 with theconfiguration shown in FIG. 21 has been described as an example, but itis essential only that soft decision value weighting be performed usinga coefficient based on the smallest value of eigenvalues calculated fromchannel fluctuation estimation results, and the reception unitconfiguration is not limited to that shown in FIG. 21, but may also beas shown in FIG. 24, for example.

[0276] The difference between reception unit 2400 in FIG. 24 andreception unit 2100 in FIG. 21 is that, whereas reception unit 2100 inFIG. 21 performs signal separation processing by means of an inversematrix computation by signal processing section 421, reception unit 2400in FIG. 24 performs MLD (Maximum Likelihood Detection) by means of softdecision value calculation section 2401, and then in error correctiondecoding section 2403 separates soft decision value signal 2402 intospread signal A received digital signal 2404 and spread signal Breceived digital signal 2405. In performing this MLD, use of eigenvaluebased coefficient 2110 enables receive data error rate characteristicsto be improved in the same way as in the above-described embodiment.

[0277] By way of example, a case will here be described in which signalsthat have undergone QPSK modulation by modulation sections 102 and 112of transmission unit 2000 shown in FIG. 20 are demodulated by performingMLD in reception unit 2400 in FIG. 24.

[0278] Soft decision value calculation section 2401, having receivedquadrature baseband signals 406 and 416, channel fluctuation estimationinformation 408, 410, 418, and 420, reception level based coefficients2115 and 2116, and eigenvalue based coefficient 2110 as input, firstcalculates received quadrature baseband signal 406 and 416 candidatesignal point positions (the present example assumes QPSK, with fourcandidate signal points provided per channel, so there are total 4×4=16candidate signal point positions) using channel fluctuation estimationinformation 408, 410, 418, and 420, thereafter finds the signal pointdistance between these candidate points and reception point, and outputsthat signal point distance weighted by reception level basedcoefficients 2115 and 2116 and eigenvalue based coefficient 2110 as softdecision value signal 2402.

[0279] The process will now be described in detail. FIG. 25(a) showssignal point position 2501 of received quadrature baseband signal 406(the signal received by antenna 401 (antenna 1)) and candidate signalpoint positions, and FIG. 25(b) shows signal point position 2502 ofreceived quadrature baseband signal 416 (the signal received by antenna411 (antenna 2)) and candidate signal point positions.

[0280] Soft decision value calculation section 2401 establishescandidate signal points of 4 transmit bits (0000), (0001), . . . ,(1111) from spread signal A channel fluctuation estimation signal 408and spread signal B channel fluctuation estimation signal 410 as shownin FIG. 25(a). Then the distance between signal point 2501 of receivedquadrature baseband signal 406 and each candidate signal point is found.In fact, the square (power value) of the signal point distance is found.Here, the squares of the signal point distances between 4 transmit bits(0000), (0001), . . . , (1111) and reception point 2501 are denoted byx0000(t), x0001(t) , x0010(t) and x1111(t) respectively.

[0281] Similarly, soft decision value calculation section 2401establishes candidate signal points of 4 transmit bits (0000), (0001), .. . , (1111) from spread signal A channel fluctuation estimation signal418 and spread signal B channel fluctuation estimation signal 420 asshown in FIG. 25(b). Then the distance between signal point 2502 ofreceived quadrature baseband signal 416 and each candidate signal pointis found. In fact, the square (power value) of the signal point distanceis found. Here, the squares of the signal point distances between 4transmit bits (0000), (0001), . . . , (1111) and reception point 2502are denoted by y0000(t), y0001(t), y0010(t), and y1111(t) respectively.

[0282] Soft decision value calculation section 2401 then performs softdecision value weighting using eigenvalue based coefficient 2110 andreception level based coefficients 2115 and 2116. To be specific,calculation is performed as follows: weighted soft decision valuez0000(t)=Ca(t)D(t) {x0000(t)+y0000(t)}. z0001(t), z0010(t), . . . ,z1111(t) are found in the same way. Ca(t) may be replaced by Cb(t). Softdecision value calculation section 2401 outputs z0001(t), z0010(t), . .. , z1111(t) weighted in this way as soft decision value signal 2402.

[0283] By performing error correction decoding of soft decision valuesignal 2402 that has undergone MLD processing and eigenvalue basedweighting processing in this way, error correction coding section 2403obtains spread signal A received digital signal 2404 and spread signal Breceived digital signal 2405, and outputs these signals.

[0284] (Embodiment 8)

[0285] In this embodiment, a case is described in which the processingdescribed in Embodiment 7 is applied to OFDM communications. A specialfeature of this embodiment is that the processing whereby soft decisionvalues are weighted using eigenvalue based coefficients calculated fromchannel fluctuation estimation results is performed for each subcarrier.

[0286]FIG. 26 shows a sample configuration of the transmission unit of atransmitting apparatus according to this embodiment. Parts in FIG. 26corresponding to parts in FIG. 10 are assigned the same codes as in FIG.10, and descriptions of parts previously described using FIG. 10 areomitted.

[0287] The difference between transmission unit 2600 in FIG. 26 andtransmission unit 1000 in FIG. 10 is that transmission unit 2600 haserror correction coding sections 2601 and 2603, which execute errorcorrection coding processing on transmit digital signals 101 and 111using convolutional code, and send error correction coded signals 2602and 2604 to modulation sections 102 and 112. By this means, transmissionunit 2600 performs OFDM processing of error correction coded data,enabling transmit data to be coded in the frequency axis direction.

[0288] Transmission unit 2600 is provided in a base station, forexample, which has a reception unit 200 as shown in FIG. 2. Transmissionunit 2600 transmits signals with the frame configurations shown in FIG.11.

[0289]FIG. 27 shows the configuration of a reception unit of thisembodiment that receives signals transmitted from transmission unit2600. Reception unit 2700 is broadly configured as a combination ofreception unit 1200 shown in FIG. 12 and reception unit 2100 shown inFIG. 21, and therefore descriptions of previously described parts inFIG. 12 and FIG. 21 are omitted here, and only parts specific to thisembodiment are described. Parts in FIG. 27 corresponding to parts inFIG. 12 are assigned the same codes as in FIG. 12.

[0290] Channel fluctuation estimation sections 1207,1209, 1217, and 1219estimate channel fluctuation on a subcarrier-by-subcarrier basis basedon estimation symbols arranged in each subcarrier. Channel fluctuationinformation generation section 2703 and eigenvalue based coefficientcalculation section 2705 find eigenvalue based coefficient 2706 for eachsubcarrier by performing the same processing as in channel fluctuationinformation generation section 426 and eigenvalue based coefficientcalculation section 2101 in FIG. 21 on a subcarrier-by-subcarrier basis,and send eigenvalue based coefficient 2706 to soft decision valuecalculation sections 2707 and 2711.

[0291] Reception level based coefficient calculation section 2701 hasoutput signals 1204 and 1214 from radio sections 1203 and 1213, outputsignals 1206 and 1216 from discrete Fourier transform sections (dft's)1205 and 1215, and output signals 1208, 1210, 1218, and 1220 fromchannel fluctuation estimation sections 1207, 1209, 1217, and 1219 asinput, and using some or all of these, finds reception level basedcoefficient 2702 for each subcarrier, and sends this coefficient 2702 tosoft decision value calculation sections 2707 and 2711.

[0292] Soft decision value calculation sections 2707 and 2711 weightinput channel A received quadrature baseband signal group 1222 andchannel B received quadrature baseband signal group 1223 by means ofeigenvalue based coefficient 2706 and reception level based coefficient2702, and output soft decision value signals 2708 and 2712. Here, softdecision value calculation sections 2707 and 2711 perform the same kindof weighting processing as described for soft decision value calculationsections 2102 and 2104 in FIG. 21 for each subcarrier. That is to say,different weighting processing is performed for each subcarrier usingthe same subcarrier received quadrature baseband signal, eigenvaluebased coefficient, and reception level based coefficient.

[0293] In this way, soft decision value signals 2708 and. 2712 weightedon a subcarrier-by-subcarrier basis are obtained, these soft decisionvalue signals 2708 and 2712 undergo error correction decoding processingby error correction decoding sections 2709 and 2713, and receiveddigital signals 2710 and 2714 are obtained.

[0294] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas a plurality of OFDM modulatedsignals transmitted from a plurality of antennas, by performingprocessing whereby soft decision values are weighted using a coefficientbased on an eigenvalue calculated from channel fluctuation estimationresults on a subcarrier-by-subcarrier basis, it is possible to give asoft decision value an appropriate likelihood based on per-subcarriereffective reception power, enabling receive data error ratecharacteristics to be improved, even when per-subcarrier effectivereception power varies due to frequency selective fading, etc.

[0295] In this embodiment a reception unit 2700 with the configurationshown in FIG. 27 has been described as an example, but it is essentialonly that per-subcarrier soft decision value weighting be performedusing a coefficient based on the smallest value of per-subcarriereigenvalues calculated from per-subcarrier channel fluctuationestimation results, and the reception unit configuration is not limitedto that shown in FIG. 27, but may also be as shown in FIG. 28, forexample.

[0296] The difference between reception unit 2800 in FIG. 28 andreception unit 2700 in FIG. 27 is that, whereas reception unit 2700 inFIG. 27 performs signal separation processing by means of an inversematrix computation by signal processing section 1221, reception unit2800 in FIG. 28 performs MLD (Maximum Likelihood Detection) by means ofsoft decision value calculation section 2801, and then in errorcorrection decoding section 2803 separates soft decision value signal2802 into received digital signal 2804 and received digital signal 2805.

[0297] As MLD processing has been described in Embodiment 7 using FIG.24, a description thereof is omitted here. However, the differencebetween above-described soft decision value calculation section 2401 inFIG. 24 and soft decision value calculation section 2801 of thisembodiment in FIG. 28 is that soft decision value calculation section2801 performs the same kind of processing as soft decision valuecalculation section 2401 on a subcarrier-by-subcarrier basis. That is tosay, soft decision value calculation section 2801 performs processing ona subcarrier-by-subcarrier basis to calculate all of candidate signalpoint positions on received quadrature baseband signal group 1206 and1216 using channel fluctuation estimation information 1208, 1210, 1218,and 1220, then finds the signal point distance between the candidatepoints and reception point on a subcarrier-by-subcarrier basis, andoutputs that signal point distance weighted by reception level basedcoefficient 2702 and eigenvalue based coefficient 2760 as soft decisionvalue signal 2802 on a subcarrier-by-subcarrier basis. In other words,per-subcarrier soft decision values are output as soft decision valuesignal 2802.

[0298] (Embodiment 9)

[0299] A special feature of this embodiment is that, in contrast toEmbodiment 7, error correction coding processing is not performedindividually on data transmitted from each antenna, but instead, data issupplied to each antenna after undergoing error correction codingprocessing by a single error correction coding section. As a result,when MLD (Maximum Likelihood Detection) processing and error correctiondecoding processing are performed on the receiving side, single-systemerror correction code is input to the MLD processing section and errorcorrection decoding section, enabling data with improved error ratecharacteristics to be obtained.

[0300]FIG. 29, in which parts corresponding to parts in FIG. 20 areassigned the same codes as in FIG. 20, shows the configuration of atransmission unit 2900 of this embodiment. The difference betweentransmission unit 2900 of this embodiment and transmission unit 2000 inFIG. 20 is that, whereas transmission unit 2000 has error correctioncoding sections 2001 and 2002 for antennas 110 and 120 respectively andperforms error correction coding processing of transmit digital signals101 and 111 individually for antennas 110 and 120, in transmission unit2900 error correction coding section 2902 first performs errorcorrection processing on transmit digital signal 2901 and then splitsthe data into error correction coded data 2903 and 2904, and supplieserror correction coded data 2903 and 2904 to modulation sections 102 and112 respectively.

[0301]FIG. 30, in which parts corresponding to parts in FIG. 24 areassigned the same codes as in FIG. 24, shows the configuration of areception unit 3000 of this embodiment. Reception unit 3000 receivessignals transmitted from transmission unit 2900. That is to say,reception unit 3000 receives signals that have undergone errorcorrection coding by the single error correction coding section 2902. Asa result, soft decision value calculation section 24.01 and errorcorrection decoding section 3001 perform error correction decodingprocessing by calculating a single-system error correction coded signalsoft decision value, and thus error correction capability is improvedcompared with a case where error correction decoding processing isperformed by calculating soft decision values separately formulti-system error correction coded signals (for example, compared withreception unit 2400 in FIG. 24). By this means, a received digitalsignal 3002 with improved error rate characteristics can be obtained.

[0302] Thus, according to this embodiment, when transmit data undergoeserror correction coding processing and is transmitted from a pluralityof antennas, transmit data is error correction coded by a single errorcorrection coding section 2902, in contrast to the configuration inEmbodiment 7, making it possible to improve error correction capabilitywhen MLD processing and error correction decoding processing areperformed on the receiving side, and enabling receive data with greatlyimproved error rate characteristics to be obtained.

[0303] (Embodiment 10)

[0304] In this embodiment, a case is described in which the specialfeature of Embodiment 9 is applied to OFDM communications.

[0305]FIG. 31 shows a sample configuration of the transmission unit of atransmitting apparatus according to this embodiment. Parts in FIG. 31corresponding to parts in FIG. 26 are assigned the same codes as in FIG.26. The difference between transmission unit 3100 of this embodiment andtransmission unit 2600 in FIG. 26 is that, whereas transmission unit2600 has error correction coding sections 2601 and 2602 for antennas 110and 120 respectively and performs error correction coding processing oftransmit digital signals 101 and 111 individually for antennas 110 and120, in transmission unit 3100 error correction coding section 3102first performs error correction processing on transmit digital signal3101 and then splits the data into error correction coded data 3103 and3104, and supplies error correction coded data 3103 and 3104 tomodulation sections 102 and 112 respectively.

[0306]FIG. 32, in which parts corresponding to parts in FIG. 28 areassigned the same codes as in FIG. 28, shows the configuration of areception unit 3200 of this embodiment. Reception unit 3200 receivessignals transmitted from transmission unit 3100. That is to say,reception unit 3200 receives signals that have undergone errorcorrection coding by the single error correction coding section 3102. Asa result, soft decision value calculation section 2801 and errorcorrection decoding section 3201 perform error correction decodingprocessing by calculating a single-system error correction coded signalsoft decision value, and thus error correction capability is improvedcompared with a case where error correction decoding processing isperformed by calculating soft decision values separately formulti-system error correction coded signals (for example, compared withreception unit 2800 in FIG. 28). By this means, a received digitalsignal 3202 with improved error rate characteristics can be obtained.

[0307] Thus, according to this embodiment, when transmit data undergoeserror correction coding processing and is transmitted from a pluralityof antennas, transmit data is error correction coded by a single errorcorrection coding section 3102, in contrast to the configuration inEmbodiment 8, making it possible to improve error correction capabilitywhen MLD processing and error correction decoding processing areperformed on the receiving side, and enabling receive data with greatlyimproved error rate characteristics to be obtained.

[0308] (Embodiment 11)

[0309] A special feature of this embodiment is that, in a receivingapparatus that performs demodulation processing using channelfluctuation matrix eigenvalues, a reception level control section isprovided that detects the signal level of each antenna received signaland makes the signal levels of the antenna received signals equal.

[0310]FIG. 33, in which parts corresponding to parts in FIG. 21 areassigned the same codes as in FIG. 21, shows the configuration of areception unit 3300 of this embodiment. Except for the provision of areception level control section 3301, reception unit 3300 has the sameconfiguration as reception unit 2100 in FIG. 21.

[0311] Reception level control section 3301 has received quadraturebaseband signals 404 and 414 as input, detects the signal levels ofthese received quadrature baseband signals 404 and 414, and sends gaincontrol signals 3302 and 3303 for equalizing the signal levels ofreceived quadrature baseband signals 404 and 414 to radio sections 403and 413. Radio sections 403 and 413 change the amplifier gain based ongain control signals 3302 and 3303.

[0312] The operation of reception unit 3300 of this embodiment will nowbe described. Reception unit 3300 performs control by means of receptionlevel control section 3301 so that the levels of the received signalsreceived by antennas 401 and 411 become equal—that is to say, so thatthe output levels of received quadrature baseband signals 404 and 414output from radio sections 403 and 413 respectively become equal.

[0313] For example, if a −40 dBm signal is received by antennas 401 and411, control is performed so that the voltages of received quadraturebaseband signals 404 and 414 are 2 V. On the other hand, if a −40 dBmsignal is received by antenna 401 and a -−46 dBm signal is received byantenna 411, control is not performed so that the voltages of receivedquadrature baseband signals 404 and 414 are both 2 V, but instead,control is performed so that the voltage of received quadrature basebandsignal 404 is 2 V and the voltage of received quadrature baseband signal414 is 1 V. In this way, the signal levels of received quadraturebaseband signals 404 and 414 are made equal.

[0314] Making the signal levels from the antennas equal in this waygreatly improves demodulation precision when performing demodulationusing channel fluctuation matrix eigenvalues, because the closer thereceived signal levels of the antennas, the greater is the significanceof a channel fluctuation matrix eigenvalue. When the signal level ofeach antenna received signal is controlled separately and control isperformed so that received quadrature baseband signals 404 and 414 havethe same voltage, the significance of an eigenvalue as an effectivereception power index decreases.

[0315] In those of the above-described embodiments in which receptionlevel based coefficients are used together with eigenvalue basedcoefficients, and demodulation is performed with these coefficients aseffective reception power indices, even if the signal levels of antennareceived signals are different, the same effect can be obtained as byequalizing reception levels, as in this embodiment, if eigenvalues arecorrected by reflecting this difference of signal levels in a receptionlevel coefficient.

[0316] Thus, according to this embodiment, in a receiving apparatus thatperforms demodulation processing using channel fluctuation matrixeigenvalues, by detecting the signal level of each antenna receivedsignal and equalizing the signal levels of the antenna received signals,the value of an eigenvalue can be made a much more appropriate value foruse as an effective reception power index, and receive data with greatlyimproved error rate characteristics can be obtained.

[0317] Control of the signal level of each antenna received signal isnot limited to application to reception unit 3300 with the configurationshown in FIG. 33, but can be widely applied to cases where demodulationprocessing is performed using eigenvalues.

[0318] (Embodiment 12)

[0319] In this embodiment, a case is described in which the specialfeature of Embodiment 11 is applied to OFDM communications.

[0320]FIG. 34, in which parts corresponding to parts in FIG. 27 areassigned the same codes as in FIG. 27, shows the configuration of areception unit 3400 of this embodiment. Except for the provision of areception level control section 3401, reception unit 3400 has a similarconfiguration to reception unit 2700 in FIG. 27.

[0321] Reception level control section 3401 has received quadraturebaseband signals 1204 and 1214 as input, detects the signal levels ofthese received quadrature baseband signals 1204 and 1214, and sends gaincontrol signals 3402 and 3403 for equalizing the signal levels ofreceived quadrature baseband signals 1204 and 1214 to radio sections1203 and 1213. Radio sections 1203 and 1213 change the amplifier gainbased on gain control signals 3402 and 3403.

[0322] By thus performing control in such a way that makes the signallevels of antenna received signals equal, the signal levels between thesubcarriers corresponding to post-Fourier-transform signals 1206 and1216 can also be made virtually equal. By this means, when modulation isperformed using channel fluctuation matrix eigenvalues on asubcarrier-by-subcarrier basis, eigenvalues for each subcarrier can bemade to reflect accurately per-subcarrier effective reception power.

[0323] Thus, according to this embodiment, in a receiving apparatus thatperforms demodulation processing using channel fluctuation matrixeigenvalues on a subcarrier-by-subcarrier basis, by detecting the signallevel of each antenna received signal and equalizing the signal levelsof the antenna received signals, the value of a per-subcarriereigenvalue can be made a much more appropriate value for use as aneffective reception power index, and OFDM receive data with greatlyimproved error rate characteristics can be obtained.

[0324] (Embodiment 13)

[0325] In this embodiment, it is proposed that space-time codedmodulated signals be transmitted from a plurality of antennas, andreceived signals be demodulated on the receiving side using channelfluctuation matrix eigenvalues. In this embodiment, in particular, areceiving antenna is selected using channel fluctuation matrixeigenvalues, and received signal demodulation is performed using onlythe space-time coded signal received by the selected receiving antenna.

[0326] Space-time coding is a known technology, and is described, forexample, in “Space-Time Block Codes from Orthogonal Design” IEEETransactions on Information Theory, pp. 1456-1467, vol. 45, no. 5, July1999.

[0327] An overview of space-time coding will be given using FIG. 35 andFIG. 36. In a communication system that uses space-time coding, transmitsignal A shown in FIG. 35 is transmitted from a transmitting antenna3601, and at the same time, transmit signal B shown in FIG. 35 istransmitted from a transmitting antenna 3602. When this is done,transmit signal A and transmit signal B transmitted from transmittingantennas 3601 and 3602 are subjected to channel fluctuations h1(t) andh2(t) respectively, and are received by a receiving antenna 3603.

[0328] In FIG. 35, reference numerals 3501 and 3504 indicate radio wavepropagation environment symbols, and reference numerals 3502, 3503,3505, and 3506 indicate coded symbol groups. Also, S1 and S2 are assumedto be different signals, and signal S1 is sent in symbol group 3502,signal -S2*, which is the negative complex conjugate of signal S 2, issent in symbol group 3503, signal S 2 is sent in symbol group 3505, andsignal S1*, which is the complex conjugate of signal S1, is sent insymbol group 3506. An asterisk (*) here indicates a complex conjugate.

[0329] The relationship between signals S1 and S2 transmitted fromtransmitting antennas 3601 and 3602, and signals R1 and R2 received byreceiving antenna 3603 can then be expressed by the following equation.

[0330] [Equation 9] $\begin{matrix}{\begin{pmatrix}{R1} \\{- {R2}^{*}}\end{pmatrix} = {\begin{pmatrix}{h1} & {h2} \\{- {h2}^{*}} & {h1}^{*}\end{pmatrix}\begin{pmatrix}{S1} \\{S2}\end{pmatrix}}} & (9)\end{matrix}$

[0331] In Equation (9), R1 is the received signal when symbol group 3502and symbol group 3505 in FIG. 35 are received, and R2 is the receivedsignal when symbol group 3503 and symbol group 3506 in FIG. 35 arereceived.

[0332] As can be seen from Equation (9), if this kind of space-timecoding technology is used, transmit signals S1 and S2 to be found can beobtained by received signal maximal-ratio combining, and therefore atransmit signal can be estimated with good precision from a receivedsignal. This concludes the overview of space-time coding technology.

[0333] The configuration of this embodiment will now be described. FIG.37, in which parts corresponding to parts in FIG. 29 described inEmbodiment 9 are assigned the same codes as in FIG. 29, shows theconfiguration of a transmission unit 3700 of a transmitting apparatusaccording to this embodiment. The difference between transmission unit2900 in FIG. 29 and transmission unit 3700 of this embodiment is thaterror correction coding section 3701 of transmission unit 3700 performsspace-time coding processing on transmit digital signal 2901 and outputsthe resulting signals. That is to say, error correction coding section3701 performs coding processing so that the relationship between errorcorrection coded signal 2903 and error correction coded signal 2904 isof the same kind as between transmit signal A and transmit signal B inFIG. 35. By this means, space-time coded signals are transmitted fromantennas 110 and 120 of transmission unit 3700.

[0334]FIG. 38 shows a configuration of a reception unit 3800 thatreceives space-time coded signals transmitted from transmission unit3700. Parts in FIG. 38 corresponding to those in FIG. 14 described inEmbodiment 3 are assigned the same codes as in FIG. 14. The differencesbetween reception unit 1400 in FIG. 14 and reception unit 3800 of thisembodiment will be described here.

[0335] Antenna selection section 1411 of reception unit 1400 ofEmbodiment 3 creates two antenna received signal combinations from threeantennas' received-signals 408, 410, 406, 418, 420, 416, 1408, 1410, and1406 containing channel estimates, finds an eigenvalue for eachcombination, and selects two antennas' received signals of thecombination for which the eigenvalue minimum power is greatest, andoutputs these as selected signals 1412, 1413, 1414, 1415, 1416, and1417.

[0336] In contrast to this, antenna selection section 3801 of receptionunit 3800 of this embodiment finds an eigenvalue for each antennareceived signal (that is, finds the Equation (9) eigenvalue for eachantenna received signal) from three antennas' received signals 408, 410,406, 418, 420, 416, 1408, 1410, and 1406 containing channel estimates,selects one antennas' received signals for which the eigenvalue minimumpower is greatest, and outputs these as selected signals 3802, 3803, and3804. The reason why it is possible to find an eigenvalue for thereceived signals of each antenna in this way is that a signal receivedat each antenna is a space-time coded signal and a channel estimationmatrix as shown in Equation (9) is obtained only for one antenna'sreceived signals.

[0337] Also, signal processing section 421 of reception unit 1400 ofEmbodiment 3 obtains two received quadrature baseband signals 422 and423 by separating input two antennas' received signals 1412, 1413, 1414,1415, 1416, and 1417 by means of the inverse matrix computation ofEquation (3).

[0338] In contrast to this, signal processing section 3805 of receptionunit 3800 of this embodiment obtains S1 and S2 received digital signal3806 by performing maximal-ratio combining of input one antennas'received signals based on Equation (9).

[0339]FIG. 39 shows the configuration of antenna selection section 3801.Antenna selection section 3801 has an eigenvalue calculation section3901 and a signal selection section 3903. Eigenvalue calculation section3901 has channel fluctuations 408 and 410, 418 and 420, and 1408 and1410, obtained from the received signals of each antenna, as input.Eigenvalue calculation section 3901 finds an Equation (9) eigenvalueusing channel fluctuations 408 and 410. Similarly, eigenvaluecalculation section 3901 finds an Equation (9) eigenvalue using channelfluctuations 418 and 420, and finds an Equation (9) eigenvalue usingchannel fluctuations 1408 and 1410. The eigenvalue minimum powers arethen compared, the antenna for which the eigenvalue minimum power isgreatest is detected, and a control signal 3902 indicating that antennais sent to signal selection section 3903.

[0340] Signal selection section 3903 outputs signals corresponding tothe antenna indicate by control signal 3902 from among signals 408, 410,and 406 obtained from the antenna 401 received signal, signals 418, 420,and 416 obtained from the antenna 411 received signal, and signals 1408,1410, and 1406 obtained from the antenna 1401 received signal, asselected signals 3602, 3603, and 3604.

[0341] The operation of reception unit 3800 of this embodiment will nowbe described. Reception unit 3800 receives space-time coded signals,transmitted from receiving antennas 110 and 120 (FIG. 37), by means ofreceiving antennas 401, 411, and 1401. Reception unit 3800 estimateschannel fluctuation values h1(t) and h2(t) for each receiving antenna.

[0342] Reception unit 3800 then calculates the channel fluctuationmatrix eigenvalue shown in Equation (9) for each receiving antenna fromthe channel fluctuation values of each receiving antenna by means ofantenna selection section 3801. Antenna selection section 3801 selectsthe antenna received signals for which the eigenvalue minimum power isgreatest. By this means, the antenna received signals for which theeffective reception power is greatest are selected. Reception unit 3800then obtains receive data by demodulating the selected antenna receivedsignals.

[0343] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas space-time coded signals transmittedfrom a plurality of antennas, by calculating channel fluctuation matrixeigenvalues of the space-time coded signals received by each antenna,selecting the antenna received signal for which the eigenvalue minimumpower is greatest, and performing demodulation processing thereupon, itis possible to select the antenna received signal with the greatesteffective reception power, enabling receive data with good error ratecharacteristics to be obtained.

[0344] In this embodiment, a case has been described in which the numberof transmitting antennas is two, and the kind of space-time code shownin FIG. 35 is used, but the number of transmitting antennas is notlimited to two, and the space-time code is not limited to that shown inFIG. 35.

[0345] (Embodiment 14)

[0346] In this embodiment, a case is described in which, as inEmbodiment 13, when space-time coded modulated signals are transmittedfrom a plurality of antennas, channel fluctuation matrix eigenvalues arefound for each antenna's received signals on the receiving side, and theantenna received signals for which the eigenvalue minimum power isgreatest are selected and undergo demodulation. However, in thisembodiment, a case is described in which the special feature ofEmbodiment 13 is applied to OFDM communications.

[0347]FIG. 40 shows frame configurations when space-time code is OFDMmodulated and transmitted. As can be seen by comparing FIG. 40 with FIG.35, space-time code is arranged in carrier 1 of the same frequency band.Mutually corresponding codes are also similarly arranged in othercarriers. Such transmit signals A and B can be formed by replacingspreading sections 104 and 114 in FIG. 37 with inverse discrete Fouriertransform sections (idft's).

[0348] In a reception unit that receives signals with the kind of framesshown in FIG. 40, despreading sections 405, 415, and 1405 in FIG. 38 canbe replaced by discrete Fourier transform sections (dft's), spreadsignal A channel fluctuation estimation sections 407, 417, and 1407 canbe replaced by channel A channel fluctuation estimation sections, andspread signal B channel fluctuation estimation sections 409, 419, and1409 can be replaced by channel B channel fluctuation estimationsections. It is assumed that the channel A channel fluctuationestimation sections estimate per-subcarrier channel fluctuation, and thechannel B channel fluctuation estimation sections similarly estimateper-subcarrier channel fluctuation.

[0349] Antenna selection section 3801 can then calculate channelfluctuation matrix eigenvalues of space-time coded signals received ateach antenna on a subcarrier-by-subcarrier basis, and select antennareceived signals for which the eigenvalue minimum power is greatest on asubcarrier-by-subcarrier basis.

[0350] In this way, the antenna for which effective reception power isgreatest can be selected on a subcarrier-by-subcarrier basis, enablingthe optimal antenna to be selected for each subcarrier. As a result,error rate characteristics can be improved for all subcarriers.

[0351] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas space-time coded OFDM modulatedsignals transmitted from a plurality of antennas, by calculating on asubcarrier-by-subcarrier basis channel fluctuation matrix eigenvalues ofthe space-time coded signals received by each antenna, selecting on asubcarrier-by-subcarrier basis the antenna received signal for which theeigenvalue minimum power is greatest, and performing demodulationprocessing thereupon, it is possible to select on asubcarrier-by-subcarrier basis the antenna received signal with thegreatest effective reception power, enabling receive data with gooderror rate characteristics to be obtained across all subcarriers.

[0352] In this embodiment, the kind of frame configuration shown in FIG.40 has been taken by way of example as the frame configuration used whenspace-time code is OFDM modulated and transmitted, but in a case wheresignals with the kind of frame configuration shown in FIG. 41 arereceived by a plurality of antennas, also, as long as an antenna isselected based on channel fluctuation matrix eigenvalues for eachreceiving antenna, antenna received signals for which the effectivereception power is greatest can be selected in the same way as in theabove embodiment, enabling the error rate characteristics of receivedata to be improved. The coding shown in FIG. 41 is generally referredto as frequency-time coding as opposed to space-time coding.

[0353] That is to say, the eigenvalue-based receiving antenna selectionmethod according to this embodiment is not limited to space-time coding,and the same kind of effect as in the above-described embodiment canalso be obtained if the present invention is applied to space-frequencycoding, or space-frequency-time coding in which space-time coding andspace-frequency coding are performed simultaneously.

[0354] (Embodiment 15)

[0355] In above-described Embodiment 13, it was proposed that, whenspace-time coded received signals are received by a plurality ofantennas, a receiving antenna be selected based on channel fluctuationmatrix eigenvalues of each antenna's received signals (that is, only onereceiving antenna be selected), and receive data be obtained bydemodulating the signals obtained by the selected receiving antenna.

[0356] In contrast to this, in this embodiment a method and apparatusare proposed whereby, when space-time coded signals are received by aplurality of antennas, each antenna's received signals are weighted andcombined based on channel fluctuation matrix eigenvalues of eachantenna's received signals, and receive data is obtained by demodulatingthe weighted and combined received signals.

[0357] The eigenvalue-based antenna received signal weighting andcombining method of this embodiment is similar to the combining methodof above-described Embodiment 5. However, the combining method of thisembodiment and the combining method of Embodiment 5 differ in thefollowing respect.

[0358] In the combining method of Embodiment 5, a plurality of antennareceived signal combinations are first created, a channel fluctuationmatrix is created for each combination, and channel fluctuation matrixeigenvalues are calculated for each combination. Then, modulated signalsare separated using the antenna received signals of each combination andthe channel fluctuation matrix corresponding to that combination, andmodulated signals separated in each combination are weighted andcombined using the channel fluctuation estimation matrix eigenvaluesused at the time of separation.

[0359] In contrast to this, in the combining method of this embodiment,a channel fluctuation matrix as shown in Equation (9) is created foreach antenna's received signals, and an eigenvalue of the channelfluctuation matrix of each antenna's received signals is calculated.Each antenna's received signals are then weighted and combined based onthese eigenvalues. In this kind of embodiment, antenna received signalcombinations are not found as in Embodiment 5, but a channel fluctuationmatrix is created individually for each antenna's received signals, andan eigenvalue is found individually for each antenna's received signals.This is possible because the received signals are space-time codedsignals.

[0360]FIG. 42, in which parts corresponding to parts in FIG. 18described in Embodiment 5 are assigned the same codes as in FIG. 18,shows the configuration of a reception unit 4200 according to thisembodiment. The difference between reception unit 1800 in FIG. 18 andreception unit 4200 of this embodiment lies in the configuration ofsignal processing section 4201. Reception unit 4200 receives space-timecoded signals as shown in FIG. 35 transmitted from transmission unit3700 shown in FIG. 37.

[0361]FIG. 43 shows the configuration of signal processing section 4201.Signal processing section 4201 has an eigenvalue calculation section4301 and a combining section 4303. Eigenvalue calculation section 4301has channel fluctuations 408 and 410, 418 and 420, and 1408 and 1410,obtained from the received signals of each antenna, as input. Eigenvaluecalculation section 4301 finds an Equation (9) eigenvalue using channelfluctuations 408 and 410. Similarly, eigenvalue calculation section 4301finds an Equation (9) eigenvalue using channel fluctuations 418 and 420,and finds an Equation (9) eigenvalue using channel fluctuations 1408 and1410. Eigenvalue calculation section 4301 then finds for each antennathe value with the minimum eigenvalue power from among the eigenvaluesfound for each antenna, and outputs the results as eigenvalue powers P1,P2, and P3 of each antenna's received signals. That is to say,eigenvalue calculation section 4301 outputs eigenvalue powers P1, P2,and P3 for each of antennas 1401, 411, and 1401 as an eigenvalueestimation signal 4302.

[0362] Combining section 4303 applies input signals 408, 410, and 406 toEquation (9), and by performing Equation (9) inverse matrix computation,finds spread signal A received quadrature baseband signal Ra1 and spreadsignal B received quadrature baseband signal Rb1. Similarly, combiningsection 4303 applies input signals 418, 420, and 416 to Equation (9),and by performing Equation (9) inverse matrix computation, finds spreadsignal A received quadrature baseband signal Ra2 and spread signal Breceived quadrature baseband signal Rb2. Similarly, combining section4303 applies input signals 1408, 1410, and 1406 to Equation (9), and byperforming Equation (9) inverse matrix computation, finds spread signalA received quadrature baseband signal Ra3 and spread signal B receivedquadrature baseband signal Rb3.

[0363] Next, combining section 4303 weights and combines these spreadsignal A received quadrature baseband signals Ra1, Ra2, and Ra3, andspread signal B received quadrature baseband signals Rb1, Rb2, and Rb3,using eigenvalue powers P1, P2, and P3 of each antenna. Specifically, ifspread signal A received quadrature baseband signal after weighting andcombining 4202 is designated Ra and spread signal B received quadraturebaseband signal after weighting and combining 4203 is designated Rb,then Ra and Rb are given by the following equations.

[0364] [Equations 10] $\begin{matrix}{{{Ra} = {\frac{1}{3\left( {{P1} + {P2} + {P3}} \right)}\left( {{{P1} \times {Ra1}} + {{P2} \times {Ra2}} + {{P3} \times {Ra3}}} \right)}}{{Rb} = {\frac{1}{3\left( {{P1} + {P2} + {P3}} \right)}\left( {{{P1} \times {Rb1}} + {{P2} \times {Rb2}} + {{P3} \times {Rb3}}} \right)}}} & (10)\end{matrix}$

[0365] By weighting and combining each antenna's received signalsaccording to eigenvalue power on an antenna-by-antenna basis in thisway, accurate spread signal A and B received quadrature baseband signalscan be obtained. This is because the channel fluctuation matrixeigenvalue power of each antenna's received signals is a valuecorresponding to the effective reception power of each antenna'sreceived signals.

[0366] Spread signal A received quadrature baseband signal 4202 andspread signal B received quadrature baseband signal 4203 obtained bysignal processing section 4201 are demodulated and decoded bydemodulation units (not shown), to become received digital signals.

[0367] By this means, data can be demodulated using spread signal A andB received quadrature baseband signals 4202 and 4203 with largeeffective reception power, enabling received digital signals withimproved error rate characteristics to be obtained.

[0368] Thus, according to this embodiment, in a receiving apparatus thatreceives at a plurality of antennas space-time coded signals transmittedfrom a plurality of antennas, by calculating channel fluctuation matrixeigenvalues of the space-time coded signals received by each antenna,and weighting and combining each antenna's received signals usingper-antenna eigenvalue power, it is possible to obtain received signalswith large effective reception power, enabling receive data with gooderror rate characteristics to be obtained.

[0369] In this embodiment a method has been described whereby channelfluctuation matrix eigenvalue power is used as a weighting coefficient,and received quadrature baseband signals are weighted and combined usingthis coefficient, but the present invention is not limited to this.

[0370] For example, channel fluctuation matrix eigenvalue powerdescribed in this embodiment may also be used as a weighting coefficientfor MLD (Maximum Likelihood Detection) shown in “A simple transmitdiversity technique for wireless communications” IEEE Journal on SelectAreas in Communications, vol. 16, no. 8, October 1998. Use of channelfluctuation matrix eigenvalue power as a weighting coefficient indemodulation and decoding when performing MLD improves receptionquality. This also applies to Embodiment 16 described below.

[0371] (Embodiment 16)

[0372] In this embodiment, a case is described in which, as inEmbodiment 15, when space-time coded modulated signals are transmitted,channel fluctuation matrix eigenvalues are found for each antenna'sreceived signals on the receiving side, and the antenna received signalsfor which the eigenvalue minimum power is greatest are selected andundergo demodulation. However, in this embodiment, a case is describedin which the special feature of Embodiment 15 is applied to OFDMcommunications.

[0373] That is to say, a receiving apparatus of this embodiment receivessignals with the frame configurations shown in FIG. 40. In the receptionunit of a receiving apparatus of this embodiment, despreading sections405, 415, and 1405 in FIG. 42 can be replaced by discrete Fouriertransform sections (dft's), spread signal A channel fluctuationestimation sections 407, 417, and 1407 can be replaced by channel Achannel fluctuation estimation sections, and spread signal B channelfluctuation estimation sections 409, 419, and 1409 can be replaced bychannel B channel fluctuation estimation sections. It is assumed thatthe channel A channel fluctuation estimation sections estimateper-subcarrier channel fluctuation, and the channel B channelfluctuation estimation sections similarly estimate per-subcarrierchannel fluctuation.

[0374] Signal processing section 4201 then calculates channelfluctuation matrix eigenvalues of space-time coded signals received ateach antenna on a subcarrier-by-subcarrier basis, and performs weightingand combining using eigenvalue power described in Embodiment 15 as aweight coefficient on a subcarrier-by-subcarrier basis.

[0375] In this way, by performing combining of each antenna's receivedsignals with eigenvalue power as a weight coefficient on acarrier-by-carrier basis, error rate characteristics can be improvedacross all carriers even when effective reception power differs greatlyfrom carrier to carrier due to the effects of frequency selectivefading, etc.

[0376] Thus, according to this embodiment, when space-time coded OFDMsignals are received at a plurality of antennas, by performingprocessing whereby received signals obtained at each receiving antennaare weighted and combined based on channel fluctuation matrixeigenvalues, as described in Embodiment 15, for each carrier, it ispossible to implement a receiving apparatus that enables the error ratecharacteristics of received space-time coded OFDM signals to be improvedacross all carriers.

[0377] (Embodiment 17)

[0378] In this embodiment, receiving-side demodulation processing isdescribed for a case where convolutional coded signals further undergospace-time block coding and are transmitted from a plurality ofantennas.

[0379]FIG. 44, in which parts corresponding to parts in FIG. 1 describedin Embodiment 1 are assigned the same codes as in FIG. 1, shows theconfiguration of a transmission unit 4400 of a transmitting apparatus ofthis embodiment. Error correction coding sections 4401 and 4405 oftransmission unit 4400 have digital signals 101 and 111 as inputrespectively, execute convolutional coding, for example, and send codeddigital signals 4402 and 4406 to a space-time block coding section 4403.

[0380] Space-time block coding section 4403 has coded digital signals4402 and 4406 as input, and by executing space-time block coding asshown in Equation (9) on these coded digital signals 4402 and 4406,outputs modulated signal A transmit digital signal 4404 (correspondingto transmit signal A in FIG. 35) and modulated signal B transmit digitalsignal 4407 (corresponding to transmit signal B in FIG. 35) with theframe configurations shown in FIG. 35.

[0381] The kind of space-time block coding method in Equation (9) isshown in “A Simple Transmit Diversity Technique for WirelessCommunications” IEEE Journal on Select Areas in Communications, vol. 16,no. 8, October 1998. Here, a case in which the number of transmittingantennas is two and the number of transmitted modulated signals is twois described by way of example, but the present invention is not limitedto this case, and a space-time block coding method in which the numberof transmitting antennas is increased is also shown in “Space-Time BlockCodes from Orthogonal Design” IEEE Transactions on Information theory,pp. 1456-1467, vol. 45, no. 5, July 1999, etc. Error correction codingsuch as convolutional coding is executed on each modulated signal.

[0382]FIG. 45, in which parts corresponding to parts in FIG. 4 areassigned the same codes as in FIG. 4, shows the configuration of thereception unit 4500 of a receiving apparatus of this embodiment. Signalseparation section 4501 of reception unit 4500 has spread signal Achannel fluctuation estimation signal 408 (corresponding to h1 ofEquation (9)), spread signal B channel fluctuation estimation signal 410(corresponding to h2 of Equation (9)), and despread received quadraturebaseband signal 406 (corresponding to R1, R2 of Equation (9)), as input,and by performing Equation (9) inverse matrix computation, findsbaseband signal 4502 (baseband estimation signal corresponding to S1 inEquation (9)) and baseband signal 4503 (baseband estimation signalcorresponding to S2 in Equation (9)), which it outputs.

[0383] An eigenvalue calculation section 4504 has spread signal Achannel fluctuation estimation signal 408 and spread signal B channelfluctuation estimation signal 410 as input, creates an Equation (9)matrix using these, calculates an eigenvalue of that matrix, and outputseigenvalue signal 4505.

[0384] Soft decision calculation section 4506 has baseband signal 4502and eigenvalue signal 4505 as input, and finds a soft decision value asshown in Equation (5) in the same way as in Embodiment 7. At this time,a soft decision value 4507 is found using a coefficient found fromeigenvalue signal 4505—for example, eigenvalue minimum power—forweighting coefficient Ca(t)×D(t) in Equation (5), and this soft decisionvalue 4507 is output. Error correction section 4508 has soft decisionvalue 4507 as input, executes error correction decoding processing onsoft decision value 4507, and outputs received digital signal 4509obtained by this means.

[0385] Similarly, soft decision calculation section 4510 has basebandsignal 4503 and eigenvalue signal 4505 as input, and finds a softdecision value as shown in Equation (6) in the same way as in Embodiment7. At this time, a soft decision value 4511 is found using a coefficientfound from eigenvalue signal 4505—for example, eigenvalue minimumpower—for weighting coefficient Cb(t)×D(t) in Equation (6), and thissoft decision value 4511 is output. Error correction section 4512 hassoft decision value 4511 as input, executes error correction decodingprocessing on soft decision value 4511, and outputs received digitalsignal 4513 obtained by this means.

[0386] Thus, according to this embodiment, in a receiving apparatus thatreceives transmit signals combining convolutional code and space-timecode, by weighting received signal soft decision values using space-timecode channel fluctuation matrix eigenvalues, it is possible to give asoft decision value an appropriate likelihood based on effectivereception power, enabling the error rate characteristics of decodedreceive data to be improved.

[0387] That is to say, according to this embodiment, it has been shownthat receive data error rate characteristics can also be improved in acase where convolutional coding and space-time block coding arecombined, if soft decision values are weighted using eigenvalues in thesame way as in Embodiment 7.

[0388] The method whereby soft decision values are weighted usingchannel fluctuation matrix eigenvalues according to the presentinvention is not limited to Embodiment 7 or this embodiment, but can bewidely applied to cases where processing is performed that separatesmultiplexed modulated signals by means of computation using channelfluctuation matrices, convolutional coding or the like is furtherexecuted, and soft decision decoding is carried out.

[0389] (Embodiment 18)

[0390] In above-described Embodiment 5, it was proposed that a pluralityof antenna received signal combinations be created, a channelfluctuation matrix be created for each combination, channel fluctuationmatrix eigenvalues be calculated for each combination, and modulatedsignals be separated using the antenna received signals of eachcombination and the channel fluctuation matrix corresponding to thatcombination, and also that modulated signals separated in eachcombination be weighted and combined using the channel fluctuationestimation matrix eigenvalues used at the time of separation.

[0391] In contrast to this, while this embodiment is the same asEmbodiment 5 in that a plurality of antenna received signal combinationsare created, a channel fluctuation matrix is created for eachcombination, channel fluctuation matrix eigenvalues are calculated foreach combination, and modulated signals are separated using the antennareceived signals of each combination and the channel fluctuation matrixcorresponding to that combination, this embodiment differs fromEmbodiment 5 in that the Euclidian distances (branch metric) betweenreception points of modulated signals separated in each combination andcandidate points are weighted and combined using the channel fluctuationmatrix eigenvalues used at the time of separation, and soft decisionvalues after weighting and combining are determined.

[0392] In this embodiment, a case is described in which signals with theframe configurations shown in FIG. 3, transmitted from transmission unit100 with the configuration shown in FIG. 1, are received.

[0393] The reception unit of this embodiment has the same configurationas reception unit 1800 in FIG. 18 described in Embodiment 5, except forthe configuration of signal processing section 1801 of reception unit1800. In this embodiment, therefore, only the configuration of thesignal processing section will be described.

[0394]FIG. 46 shows the configuration of a signal processing section4600 according to this embodiment. In the reception unit of thisembodiment, signal processing section 1801 of reception unit 1800 inFIG. 18 is replaced by signal processing section 4600 in FIG. 46.

[0395] Eigenvalue calculation section 4608 of signal processing section4600 applies channel fluctuation estimation signals 408, 410, 418, and420 as a first group to an Equation (3) matrix, finds value P1 with thesmallest matrix eigenvalue power, and outputs this eigenvalue power P1.Similarly, eigenvalue calculation section 4608 applies channelfluctuation estimation signals 408, 410, 1408, and 1410 as a secondgroup to an Equation (3) matrix, finds value P2 with the smallest matrixeigenvalue power, and outputs this eigenvalue power P2. Similarly,eigenvalue calculation section 4608 applies channel fluctuationestimation signals 418, 420, 1408, and 1410 as a third group to anEquation (3) matrix, finds value P3 with the smallest matrix eigenvaluepower, and outputs this eigenvalue power P3.

[0396] A signal separation section 4601 applies signals 408, 410, 406,418, 420, and 416 to Equation (3) as a first group, and by performingthis inverse matrix computation, finds spread signal A receivedquadrature baseband signal 4602 (Ra1) and spread signal B receivedquadrature baseband signal 4605 (Rb1), and outputs these signals 4602and 4605. Similarly, signal separation section 4601 applies signals 408,410, 406, 1408, 1410, and 1406 to Equation (3) as a second group, and byperforming this inverse matrix computation, finds spread signal Areceived quadrature baseband signal 4603 (Ra2) and spread signal Breceived quadrature baseband signal 4606 (Rb2), and outputs thesesignals 4603 and 4606. Similarly, signal separation section 4601 appliessignals 418, 420, 416, 1408, 1410, and 1406 to Equation (3) as a thirdgroup, and by performing this inverse matrix computation, finds spreadsignal A received quadrature baseband signal 4604 (Ra3) and spreadsignal B received quadrature baseband signal 4607 (Rb3), and outputsthese signals 4604 and 4607.

[0397] Soft decision value calculation section 4609 has spread signal Areceived quadrature baseband signal 4602 (Ra1) and eigenvalue powersignal (P1) as input, finds soft decision value 4610 by weightingreceived quadrature baseband signal 4602 (Ra1) with eigenvalue powersignal (P1), and outputs this soft decision value 4610. The operation atthis time will be described using FIG. 47.

[0398]FIG. 47 is a drawing showing the QPSK signal point arrangement inthe in-phase I-orthogonal Q plane, in which reference numeral 4701indicates QPSK signal points, and [0,0], [0,1], 1,0], and [1,1] indicatetransmit bits. Reference numeral 4702 indicates the position of areceived quadrature baseband signal, and here shows the position ofspread signal A received quadrature baseband signal 4602 (Ra1). TheEuclidian distances between QPSK signal points 4701 and receivedquadrature baseband signal 4602 (Ra1) are designated D1[0,0], D1[0,1],D1[1,0], and D1[1,1]. Soft decision value calculation section 4609 findsP1×D1 ² [0,0], P1×D1 ²[0,1],P1×D1 ²[1.0], and P1×D1 ²[ 1,1], and outputsthese as soft decision value signal 4610.

[0399] Similarly, soft decision value calculation section 4611 hasspread signal A received quadrature baseband signal 4603 (Ra2) andeigenvalue power signal (P2) as input, finds soft decision value 4612 byweighting received quadrature baseband signal 4603 (Ra2) with eigenvaluepower signal (P2), and outputs this soft decision value 4612. Actually,if the Euclidian distances between QPSK signal points 4701 and receivedquadrature baseband signal 4603 (Ra2) in FIG. 47 are designated D2[0,0],D2[0,1], D2[1,0], and D2[1,1], soft decision value calculation section4611 finds P2×D2 ²[0,0], P2×D2 ²[0,1], P2×D2 ²[1,0], and P2×D2 ²[1,1],and outputs these as soft decision value signal 4612.

[0400] Similarly, soft decision value calculation section 4613 hasspread signal A received quadrature baseband signal 4604 (Ra3) andeigenvalue power signal (P3) as input, finds soft decision value 4614 byweighting received quadrature baseband signal 4604 (Ra3) with eigenvaluepower signal (P3), and outputs this soft decision value 4614. Actually,if the Euclidian distances between QPSK signal points 4701 and receivedquadrature baseband signal 4604 (Ra3) in FIG. 47 are designated D3[0,0],D3[0,1], D3[1,0], and D3[1,1], soft decision value calculation section4613 finds P3×D3 ²[0,0], P3×D3 ²[0,1], P3×D3 ²[1,0], and P3×D3 ²[1,1],and outputs these as soft decision value signal 4614.

[0401] Thus, soft decision value calculation sections 4609, 4611, and4613 perform computations whereby the Euclidian distances between thereception points of modulated signals separated in each combination andcandidate points are weighted using the channel fluctuation matrixeigenvalues used at the time of separation.

[0402] Decision section 4621 has soft decision value signals 4610, 4612,and 4614 as input, and finds P1×D1 ²[0,0]+P2×D2 ²[0,0]+P3×D3 ²[0,0],P1×D1 ²[0,1]+P2×D2 ²[0,1]+P3×D3 ²[0,1], P1×D1 ²[1,0]+P2×D2 ²[1,0]+P3×D3²[1,0], and P1×D1 ²[1,1]+P2×D2 ²[1,1]+P3×D3 ²[1,1]. Then decisionsection 4621 searches for the smallest of the four values obtained, and,if, for example, P1×D1 ²[0,0]+P2×D2 ²[0,0]+P3×D3 ²[0,0] is the smallestvalue, decides that the transmit bits are [0,0], and outputs this asreceived digital signal 4622.

[0403] The soft decision value calculations and decision operation forspread signal A by soft decision value calculation sections 4609, 4611,and 4613 and decision section 4621 have been described above. For spreadsignal B, the same kind of soft decision value calculations and decisionoperation are performed by soft decision value calculation sections4615, 4617, and 4619, and decision section 4623, and received digitalsignal 4624 is obtained.

[0404] Thus, according to this embodiment, by creating a plurality ofantenna received signal combinations, creating a channel fluctuationmatrix for each combination, calculating channel fluctuation matrixeigenvalues for each combination, separating modulated signals using theantenna received signals of each combination and the channel fluctuationmatrix corresponding to that combination, weighting and combining theEuclidian distances (branch metric) between reception points ofmodulated signals separated in each combination and candidate pointsusing the channel fluctuation matrix eigenvalues used at the time ofseparation, and taking the candidate signal point for which theEuclidian distance is smallest as a reception point, bit decisionprocessing can be performed in which likelihood can be made higher thegreater the effective reception power of an antenna's received signals,and receive data error rate characteristics can be improved.

[0405] Thus, this embodiment coincides with Embodiment 5 in that antennareceived signals are separated on a combination-by-combination basis,and separated antenna received signals are weighted and combined usingeigenvalues on a combination-by-combination basis, but differs in themethod of weighting and combining.

[0406] Comparing this embodiment with Embodiment 5, the method ofEmbodiment 5 has the advantage of having fewer computations to findEuclidian distances than this embodiment, with the result that thecircuitry is smaller in scale. From the standpoint of error ratecharacteristics, on the other hand, this embodiment is superior toEmbodiment 5. In any case, both this embodiment and Embodiment 5 enableexcellent error rate characteristics to be obtained by using eigenvaluesas weighting coefficients.

[0407] This embodiment can also be applied to OFDM communications. Acase in which this embodiment is applied to OFDM communications can beconsidered as combining the descriptions of this embodiment andEmbodiment 6. That is to say, the method of this embodiment should beperformed on a subcarrier-by-subcarrier basis.

[0408] The method according to the present embodiment can be applied tocases where received signals are applied error correction codes such asconvolutional code, turbo code, and low density parity code. Thedecoding in this case is executed by finding a branch metric and a pathmetric sequentially based on weighted results.

[0409] (Embodiment 19)

[0410] In this embodiment, a reception method is proposed in which errorcorrection decoding processing is added to the reception method ofEmbodiment 18. That is to say, the transmitting side transmits signalssubjected to error correction coding using convolutional code, etc., asdescribed in Embodiment 7, and the receiving side weights and combinesreceived signals using eigenvalues as described in Embodiment 18, andthen performs error correction decoding processing.

[0411] A receiving apparatus of this embodiment has error correctioncoding sections 2001 and 2002 as shown in FIG. 20 and described inEmbodiment 7, and receives signals transmitted by transmission unit 2000that transmits convolutional coded signals.

[0412] The reception unit of this embodiment has the same configurationas reception unit 1800 in FIG. 18 described in Embodiment 5, except forthe configuration of signal processing section 1801 of reception unit1800. In this embodiment, therefore, only the configuration of thesignal processing section will be described.

[0413]FIG. 48 shows the configuration of a signal processing section4800 according to this embodiment. In the reception unit of thisembodiment, signal processing section 1801 of reception unit 1800 inFIG. 18 is replaced by signal processing section 4800 in FIG. 48.

[0414] In signal processing section 4800 of this embodiment, decisionsections 4621 and 4623 in FIG. 46 described in Embodiment 18 are simplyreplaced by error correction sections 4801 and 4803; other parts areassigned the same codes as in FIG. 46 and descriptions thereof areomitted.

[0415] Error correction section 4801 has soft decision value signals4610, 4612, and 4614 as input, finds a metric from P1×D1 ²[0,0]+P2×D2²[0,0]+P3×D3 ²[0,0], P1×D1 ²[0,1]+P2×D2 ²[0,1]+P3×D3 ²[0,1], P1×D1²[1,0]+P2×D2 ²[1,0]+P3×D3 ²[1,0], and P1×D1 ²[1,1]+P2×D2 ²[1,1]+P3×D3²[1,1], obtains a received digital signal 4802 by performing Viterbidecoding, for example, and performing error correction, and outputs thisreceived digital signal 4802.

[0416] In the same way as error correction section 4801, errorcorrection section 4803 also finds a metric from the Euclidian distancesfrom candidate signal points weighted and combined by means ofeigenvalues, obtains a received digital signal 4804 by performing errorcorrection such as Viterbi decoding, for example, and outputs thisreceived digital signal 4804.

[0417]FIG. 49 shows simulation results for this embodiment. In thissimulation, the relationship between Eb/No (bit-to-noise spectraldensity ratio) and BER (bit error rate) was investigated when usingconvolutional code and 2, 3, and 4 receiving antennas, as an example. InFIG. 49, reference numeral 4901 indicates the characteristic with tworeceiving antennas, reference numeral 4902 the characteristic with threereceiving antennas, and reference numeral 4903 the characteristic withfour receiving antennas. As can be seen from FIG. 49, using theconfiguration of this embodiment enables extremely good error ratecharacteristics to be obtained, especially in proportion to the numberreceiving antennas.

[0418] Thus, according to this embodiment, by performing errorcorrection decoding processing in addition to providing theconfiguration of Embodiment 18, it is possible to obtain extremely gooderror rate characteristics.

[0419] In this embodiment, a method has been described that combines themethod of Embodiment 18 with soft decision decoding, but the same kindof effect can also be obtained with a method combining the method ofEmbodiment 5 and soft decision decoding.

[0420] (Other Embodiments)

[0421] In the above-described embodiments, the descriptions havecentered on a receiving apparatus that performs demodulation processingthat takes effective reception power into consideration by using channelfluctuation matrix eigenvalues. Here, an eigenvalue may be useddirectly, or may be used after approximation. Approximation methods forfinding an eigenvalue include a method whereby approximation is executedon channel fluctuation matrix elements, such as finding an eigenvalue bymaking the power of each element of a channel fluctuation matrix equal,for example. When approximation by making the power of each element of achannel fluctuation matrix equal is performed, an eigenvalue is foundonly at the phase of each element of a channel fluctuation matrix.Therefore, control of antenna selection, antenna combining, decoding,and so forth, is performed taking only the phase of each element of thechannel fluctuation matrix into consideration. In this case, it is notnecessarily essential to perform common control of the signal level ofeach antenna.

[0422] In other words, according to the decoding method usingeigenvalues in the present embodiment, there are generally two methodsof obtaining an eigenvalue that accurately reflects effective receptionpower. One method is to correct received signal levels so as to make thereceived signal levels at respective antennas virtually equal and tocorrect an eigenvalue in accordance with the received signal levels. Theother method is to find an eigenvalue only from the phase of eachelement in channel fluctuation.

[0423] Also, in the above descriptions of a soft decision decodingmethod using eigenvalues, eigenvalue minimum power is used as aweighting coefficient, but the present invention is not limited to this,and it is also possible, for example, to input an eigenvalue and find aweighting coefficient from that eigenvalue. However, when eigenvalueminimum power is used as a weighting coefficient, receive data withextremely good error rate characteristics is obtained.

[0424] Furthermore, in the above-described embodiments, a case has beendescribed in which soft decision decoding is performed with eigenvalueminimum power as a weighting coefficient, but error rate characteristicscan also be improved if eigenvalue minimum power is used as a weightingcoefficient in hard decision decoding.

[0425] The present invention is not limited to the above-describedembodiments, and various variations and modifications may be possiblewithout departing from the scope of the present invention.

[0426] This application is based on Japanese Patent Applications No.2002-329453 filed on Nov. 13, 2002, No. 2002-374393 filed on Dec. 25,2002, No. 2003-018761 filed on Jan. 28, 2003, and No. 2003-366249 filedon Oct. 27, 2003, entire content of which is expressly incorporated byreference herein.

What is claimed is:
 1. A receiving apparatus used in a communicationsystem that has a transmitting apparatus that transmits differentmodulated signals from a plurality of antennas and a receiving apparatusthat receives modulated signals transmitted from said plurality ofantennas and demodulates each modulated signal, said receiving apparatuscomprising: a channel fluctuation estimation section that estimateschannel fluctuation values of received said plurality of modulatedsignals; an effective reception power calculation section that finds aneffective reception power value of said modulated signals based on anestimated channel fluctuation value; and a demodulation section thatperforms received signal demodulation processing using a calculatedeffective reception power value.
 2. The receiving apparatus according toclaim 1, wherein: said effective reception power calculation sectioncalculates an eigenvalue of a channel fluctuation matrix that has saidchannel fluctuation value as an element and takes that eigenvalue as anindex of said effective reception power value; and said demodulationsection performs received signal demodulation processing using saideigenvalue.
 3. The receiving apparatus according to claim 1, whereinsaid effective reception power calculation section finds effectivereception power of said modulated signals using received field strengthat each antenna in addition to said channel fluctuation value.
 4. Thereceiving apparatus according to claim 2, wherein: modulated signalstransmitted from said plurality of antennas are received at a pluralityof antennas; said effective reception power calculation section, incalculating said eigenvalue, creates a plurality of combinations of saidplurality of antenna received signals, forms a channel fluctuationmatrix for each combination, and calculates an eigenvalue of a channelfluctuation matrix of each combination; and said demodulation sectionselects a combination of antenna received signals for which minimumpower of said eigenvalue is greatest and performs demodulationprocessing thereon.
 5. The receiving apparatus according to claim 2,wherein: modulated signals transmitted from said plurality of antennasare received at a plurality of antennas; said effective reception powercalculation section, in calculating said eigenvalue, creates a pluralityof combinations of said plurality of antenna received signals, forms achannel fluctuation matrix for each combination, and calculates aneigenvalue of a channel fluctuation matrix of each combination; and saiddemodulation section separates each modulated signal using eachcombination of antenna received signals and said channel fluctuationmatrix corresponding to that combination, and also performs weightingand combining of modulated signals separated in each combination using achannel fluctuation matrix eigenvalue used at the time of separation. 6.The receiving apparatus according to claim 2, wherein said demodulationsection comprises: a soft decision value calculation section thatcalculates a weighted soft decision value using said eigenvalue; and adecoding section that obtains a digital signal from a weighted softdecision value.
 7. The receiving apparatus according to claim 2, furthercomprising a received field strength detection section that detectsreceived field strength of said each antenna received signal; whereinsaid demodulation section performs demodulation processing of a receivedsignal using said eigenvalue corrected in accordance with received fieldstrength of each antenna received signal.
 8. The receiving apparatusaccording to claim 2, further comprising a received field strengthdetection section that detects received field strength of said eachantenna received signal; wherein said effective reception powercalculation section, in calculating said eigenvalue, corrects saidchannel fluctuation matrix based on received field strength of eachantenna received signal so that power of said each channel fluctuationvalue becomes equal, and calculates said eigenvalue using a correctedchannel fluctuation matrix.
 9. The receiving apparatus according toclaim 2, wherein modulated signals transmitted from said plurality ofantennas are received at a plurality of antennas, and further comprisinga reception level control section that detects received field strengthof said each antenna received signal and makes a reception level of saideach antenna received signal equal.
 10. The receiving apparatusaccording to claim 2, wherein said receiving apparatus receives a signalcoded by means of coding processing comprising any one of space-timecoding, space-frequency coding, or space-time-frequency coding.
 11. Atransmitting apparatus used in a communication system that has atransmitting apparatus that transmits different modulated signals from aplurality of antennas and a receiving apparatus that receives modulatedsignals transmitted from said plurality of antennas and demodulates eachmodulated signal, said transmitting apparatus comprising: a modulationsection that forms a modulated signal transmitted from each antenna; areceiving section that receives from said receiving apparatus feedbackinformation indicating channel fluctuation when said each modulatedsignal is received; and a transmission power control section thatmodifies, independently for each antenna, transmission power of amodulated signal transmitted from each antenna based on said feedbackinformation.
 12. The transmitting apparatus according to claim 11,wherein: said feedback information includes information indicatingchannel fluctuation of each modulated signal between each antenna ofsaid transmitting apparatus and each antenna of said receivingapparatus, and information indicating received field strength of eachantenna of said receiving apparatus; and said transmission power controlsection modifies transmission power of a modulated signal transmittedfrom each antenna based on said channel fluctuation and said receivedfield strength.
 13. The transmitting apparatus according to claim 11,wherein: said modulation section forms an OFDM signal as said modulatedsignal; and said transmission power control section modifiestransmission power of a modulated signal transmitted from each antennaindependently for each antenna and independently for each carrier basedon said feedback information.
 14. The transmitting apparatus accordingto claim 13, wherein: said feedback information includes informationindicating channel fluctuation of each carrier; and said transmissionpower control section modifies transmission power of each OFDM signalindependently in each carrier based on said channel fluctuation of eachcarrier.
 15. The transmitting apparatus according to claim 13, wherein:said feedback information includes information indicating channelfluctuation and received field strength of each carrier; and saidtransmission power control section modifies transmission power of eachOFDM signal independently for each carrier based on said channelfluctuation and received field strength of each carrier.
 16. Thetransmitting apparatus according to claim 11, wherein said transmissionpower control section modifies transmission power based on an eigenvalueof a channel fluctuation matrix indicating said channel fluctuation. 17.The receiving apparatus according to claim 2, said receiving apparatusfurther comprising a transmitting section that transmits said channelfluctuation value or said eigenvalue to a transmitting apparatus. 18.The receiving apparatus according to claim 1, said receiving apparatusfurther comprising a transmitting section that transmits said channelfluctuation value, said eigenvalue, or said received field strength to atransmitting apparatus.
 19. A reception method whereby modulated signalstransmitted from a plurality of antennas are received and each modulatedsignal is demodulated, said reception method comprising: a step ofestimating channel fluctuation values of received said plurality ofmodulated signals; a step of finding, based on an estimated channelfluctuation value, an eigenvalue of a channel fluctuation matrix ofwhich that channel fluctuation value is an element; and a step ofperforming received signal demodulation processing using a calculatedeigenvalue.